Oct. 27, 2017

Janus Investment Fund

Janus Henderson Value Plus Income Fund

Supplement dated July 2, 2018

to Currently Effective Prospectuses

On June 21, 2018, the Board of Trustees of Janus Henderson Value Plus Income Fund (the “Fund”) approved changes to the principal investment strategies and tertiary benchmark index of the Fund, among other matters. These changes are effective on or about August 31, 2018.

1. The Fund’s tertiary benchmark index will change as follows:

The Fund will change the underlying composition of the Value Income Index, the Fund’s tertiary benchmark index, to reflect the total returns from the Russell 1000^® Value Index (40%) and the Bloomberg Barclays U.S. Aggregate Bond Index (60%), replacing the current underlying composition of the Value Income Index which reflects the total returns from the Russell 1000^® Value Index (50%) and the Bloomberg Barclays U.S. Aggregate Bond Index (50%). The Fund will continue to retain the Russell 1000^® Value Index as its primary benchmark index and the Bloomberg Barclays U.S. Aggregate Bond Index as its secondary benchmark index.

2. The following replaces in its entirety the information under “Principal Investment Strategies” in the Fund Summary section of the Fund’s Prospectuses:

The Fund pursues its investment objective by normally investing 50-60% of its assets in fixed-income securities and investing the remainder in equity securities and cash equivalents.

Fixed-Income Securities.  The Fund’s fixed-income investments generate total return from a combination of current income and capital appreciation, but income is usually the dominant portion. The Fund normally invests the portion of its assets allocated to fixed-income investments in a multi-sector portfolio of U.S. and non-U.S. debt securities that the fixed-income portfolio managers believe have high income potential. The Fund may invest up to 65% of the fixed-income portion of its assets in high-yield/high-risk bonds, also known as “junk” bonds. The Fund’s fixed-income investment sectors include, but are not limited to: (i) government notes and bonds; (ii) corporate bonds, including high-yield/high-risk bonds; (iii) commercial loans; (iv) commercial and residential mortgage-backed securities; (v) asset-backed securities; (vi) convertible securities and preferred stock; and (vii) emerging market debt. The Fund’s fixed-income portfolio managers believe that by investing in multiple sectors that potentially have low correlation to each other, the volatility of the Fund’s fixed-income portion may be reduced. The Fund may not have exposure to all of these investment sectors, and the Fund’s exposure to any one investment sector will vary over time. The Fund may also invest in money market instruments and zero-coupon bonds. The Fund will typically enter into “to be announced” or “TBA” commitments when purchasing mortgage-backed securities or other securities.

In addition to considering economic factors such as the effect of interest rates on the Fund’s fixed-income investments, the Fund’s fixed-income portfolio managers apply a “bottom up” approach in choosing investments. This means that the portfolio managers look at income-producing securities one at a time to determine if a security is an attractive investment opportunity and if it is consistent with the Fund’s investment policies. The Fund’s fixed-income portfolio managers additionally consider the expected risk-adjusted return on a particular investment and the Fund’s overall risk allocations and volatility.

Equity Securities.  The Fund’s equity investments generate total return from a combination of capital appreciation and current income. Such equity investments may include companies of any size, but the Fund will invest primarily in large- and mid-sized companies whose stock prices the portfolio managers believes to be undervalued or have the potential for high relative dividend yields, or both. The Fund’s equity portfolio managers invest in companies which have fallen out of favor with the market or that appear to be temporarily misunderstood by the investment community. The Fund’s equity portfolio managers generally look for companies with:

• strong balance sheets and solid recurring free cash flows;

• attractive relative and absolute valuation ratios or that have underperformed recently; and

• favorable reward to risk characteristics.

The Fund may also invest in foreign securities, which may include investments in emerging markets.

The Fund may also invest its assets in derivatives, which are instruments that have a value derived from, or directly linked to, an underlying asset, such as equity securities, fixed-income securities, commodities, currencies, interest rates, or market indices. In particular, the Fund may buy and sell put and call options to enhance returns, utilize interest rate futures to manage portfolio risk, use forward currency contracts to manage currency risk, and use index and single-name credit default swaps to manage portfolio risk and enhance returns. The Fund may also enter into short positions for hedging purposes and to enhance returns.

Janus Capital manages the Fund’s fixed-income investments and Perkins manages the Fund’s equity investments. The Fund’s portfolio managers collaborate in determining the Fund’s overall asset allocation. The Fund may periodically adjust its mix of equity and fixed-income investments in response to changing economic and market conditions, including outside the range of 50-60% of its assets in fixed-income securities. Due to the nature of the fixed-income securities in which the Fund invests, it may have relatively high portfolio turnover compared to other funds.

3. The following replaces in its entirety the information under “Principal Investment Risks” in the Fund Summary section of the Fund’s Prospectuses:

The biggest risk is that the Fund’s returns and yields will vary, and you could lose money. The Fund is designed for long-term investors seeking a portfolio including common stocks and bonds selected for their potential to produce capital appreciation and current income. Common stocks tend to be more volatile than many other investment choices.

Fixed-Income Securities Risk.  The Fund invests in a variety of fixed-income securities. Typically, the values of fixed-income securities change inversely with prevailing interest rates. Therefore, a fundamental risk of fixed-income securities is interest rate risk, which is the risk that the value of such securities will generally decline as prevailing interest rates rise, which may cause the Fund’s net asset value to likewise decrease. For example, while securities with longer maturities and durations tend to produce higher yields, they also tend to be more sensitive to changes in prevailing interest rates and are therefore more volatile than shorter-term securities and are subject to greater market fluctuations as a result of changes in interest rates. Further, during periods of very low or negative interest rates, the Fund may not be able to maintain positive returns. The Fund may be subject to heightened interest rate risk because the Federal Reserve has ended its monetary stimulus program known as quantitative easing and interest rates are near historically low levels. Since December 2016, the Federal Reserve has begun to raise the target range for the federal funds rate. To the extent the Federal Reserve continues to raise rates, there is a risk that the fixed-income markets will experience increased volatility and that the liquidity of certain Fund investments may be reduced. These developments could cause the Fund’s net asset value to fluctuate or make it more difficult for the Fund to accurately value its securities. These developments or others also could cause the Fund to face increased shareholder redemptions, which may lead to increased portfolio turnover and transaction costs, or could force the Fund to liquidate investments at disadvantageous times or prices, therefore adversely affecting the Fund as well as the value of your investment. The amount of assets deemed illiquid remaining within the Fund may also increase, making it more difficult to meet shareholder redemptions and further adversely affecting the value of the Fund. How specific fixed-income securities may react to changes in interest rates will depend on the specific characteristics of each security. Fixed-income securities are also subject to credit risk, prepayment risk, valuation risk, extension risk, and liquidity risk.

Credit risk is the risk that the credit strength of an issuer of a fixed-income security will weaken and/or that the issuer will be unable to make timely principal and interest payments and that the security may go into default. Prepayment risk is the risk that during periods of falling interest rates, certain fixed-income securities with higher interest rates, such as mortgage- and asset-backed securities, may be prepaid by their issuers thereby reducing the amount of interest payments. Valuation risk is the risk that one or more of the fixed-income securities in which the Fund invests are priced differently than the value realized upon such security’s sale. In times of market instability, valuation may be more difficult. Extension risk is the risk that borrowers may pay off their debt obligations more slowly in times of rising interest rates, which will lengthen the duration of the portfolio. Liquidity risk is the risk that fixed-income securities may be difficult or impossible to sell at the time that the portfolio managers would like or at the price the portfolio managers believe the security is currently worth. Liquidity risk may be increased to the extent that the Fund invests in Rule 144A and restricted securities.

High-Yield/High-Risk Bond Risk.  High-yield/high-risk bonds (also known as “junk” bonds) may be more sensitive than other types of bonds to economic changes, political changes, or adverse developments specific to the company that issued the bond, which may adversely affect their value. High-yield/high-risk bonds are bonds rated below investment grade by the primary rating agencies such as Standard & Poor’s Ratings Services, Fitch, Inc., and Moody’s Investors Service, Inc. or are unrated bonds of similar quality. The value of lower quality bonds generally is more dependent on credit risk than investment grade bonds. Issuers of high-yield/high-risk bonds may not be as strong financially as those issuing bonds with higher credit ratings and are more vulnerable to real or perceived economic changes, political changes, or adverse developments specific to the issuer. In addition, the junk bond market can experience sudden and sharp price swings.

Market Risk.  The value of the Fund’s portfolio may decrease if the value of an individual company or security, or multiple companies or securities, in the portfolio decreases or if the portfolio managers’ belief about a company’s intrinsic worth is incorrect. Further, regardless of how well individual companies or securities perform, the value of the Fund’s portfolio could also decrease if there are deteriorating economic or market conditions. It is important to understand that the value of your investment may fall, sometimes sharply, in response to changes in the market, and you could lose money. Market risk may affect a single issuer, industry, economic sector, or the market as a whole.

Value Investing Risk.  Because different types of stocks tend to shift in and out of favor depending on market and economic conditions, “value” stocks may perform differently than other types of stocks and from the market as a whole, and can continue to be undervalued by the market for long periods of time. It is also possible that a value stock will never appreciate to the extent expected by the equity portfolio manager.

Mid-Sized Companies Risk.  The Fund’s investments in securities issued by mid-sized companies may involve greater risks than are customarily associated with larger, more established companies. Securities issued by mid-sized companies tend to be more volatile than securities issued by larger or more established companies and may underperform as compared to the securities of larger companies.

Mortgage- and Asset-Backed Securities Risk.  Mortgage- and asset-backed securities represent interests in “pools” of commercial or residential mortgages or other assets, including consumer loans or receivables. Mortgage- and asset-backed securities tend to be more sensitive to changes in interest rates than other types of debt securities. Investments in mortgage- and asset-backed securities are subject to both extension risk, where borrowers pay off their debt obligations more slowly in times of rising interest rates, and prepayment risk, where borrowers pay off their debt obligations sooner than expected in times of declining interest rates. These risks may reduce the Fund’s returns. In addition, investments in mortgage- and asset-backed securities, including those comprised of subprime mortgages, may be subject to a higher degree of credit risk, valuation risk, and liquidity risk than various other types of fixed-income securities.

TBA Commitments Risk.  The Fund will typically enter into “to be announced” or “TBA” commitments for mortgage-backed securities and, at times, the portion of the Fund’s portfolio allocated to TBA securities may be significant. There can be no assurance that a security purchased on a forward commitment basis will ultimately be issued or delivered by the counterparty. During the settlement period, the Fund will still bear the risk of any decline in the value of the security to be delivered. Because TBA commitments do not require the purchase and sale of identical securities, the characteristics of the security delivered to the Fund may be less favorable than the security delivered to the dealer. If the counterparty to a transaction fails to deliver the securities, the Fund could suffer a loss. At the time of its acquisition, a TBA security may be valued at less than the purchase price.

Loan Risk.  The Fund may invest in a variety of loans. Bank loans are obligations of companies or other entities entered into in connection with recapitalizations, acquisitions, and refinancings. The Fund’s investments in bank loans are generally acquired as a participation interest in, or assignment of, loans originated by a lender or other financial institution. These investments may include institutionally-traded floating and fixed-rate debt securities. The bank loans underlying these securities often involve borrowers with low credit ratings whose financial conditions are troubled or uncertain, including companies that are highly leveraged or in bankruptcy proceedings. Participation interests and assignments involve credit, interest rate, and liquidity risk.

Sovereign Debt Risk.  The Fund may invest in U.S. and non-U.S. government debt securities (“sovereign debt”). Some investments in sovereign debt, such as U.S. sovereign debt, are considered low risk. However, investments in sovereign debt, especially the debt of less developed countries, can involve a high degree of risk, including the risk that the governmental entity that controls the repayment of sovereign debt may not be willing or able to repay the principal and/or to pay the interest on its sovereign debt in a timely manner. A sovereign debtor’s willingness or ability to satisfy its debt obligation may be affected by various factors including, but not limited to, its cash flow situation, the extent of its foreign currency reserves, the availability of foreign exchange when a payment is due, and the relative size of its debt position in relation to its economy as a whole. In the event of default, there may be limited or no legal remedies for collecting sovereign debt and there may be no bankruptcy proceedings through which the Fund may collect all or part of the sovereign debt that a governmental entity has not repaid. In addition, to the extent the Fund invests in non-U.S. sovereign debt, it may be subject to currency risk.

Foreign Exposure Risk.  The Fund may have exposure to foreign markets as a result of its investments in foreign securities, including investments in emerging markets, which can be more volatile than the U.S. markets. As a result, its returns and net asset value may be affected to a large degree by fluctuations in currency exchange rates or political or economic conditions in a particular country. In some foreign markets, there may not be protection against failure by other parties to complete transactions. It may not be possible for the Fund to repatriate capital, dividends, interest, and other income from a particular country or governmental entity. In addition, a market swing in one or more countries or regions where the Fund has invested a significant amount of its assets may have a greater effect on the Fund’s performance than it would in a more geographically diversified portfolio. To the extent the Fund invests in foreign debt securities, such investments are sensitive to changes in interest rates. Additionally, investments in securities of foreign governments involve the risk that a foreign government may not be willing or able to pay interest or repay principal when due. The Fund’s investments in emerging market countries may involve risks greater than, or in addition to, the risks of investing in more developed countries.

Emerging Markets Risk.  The risks of foreign investing mentioned above are heightened when investing in emerging markets. Emerging markets securities involve a number of additional risks, which may result from less government supervision and regulation of business and industry practices (including the potential lack of strict finance and accounting controls and standards), stock exchanges, brokers, and listed companies, making these investments potentially more volatile in price and less liquid than investments in developed securities markets, resulting in greater risk to investors. There is a risk in developing countries that a future economic or political crisis could lead to price controls, forced mergers of companies, expropriation or confiscatory taxation, imposition or enforcement of foreign ownership limits, seizure, nationalization, sanctions or imposition of restrictions by various governmental entities on investment and trading, or creation of government monopolies, any of which may have a detrimental effect on the Fund’s investments. In addition, the Fund’s investments may be denominated in foreign currencies and therefore, changes in the value of a country’s currency compared to the U.S. dollar may affect the value of the Fund’s investments. To the extent that the Fund invests a significant portion of its assets in the securities of issuers in or companies of a single country or region, it is more likely to be impacted by events or conditions affecting that country or region, which could have a negative impact on the Fund’s performance. Some of the risks of investing directly in foreign and emerging market securities may be reduced when the Fund invests indirectly in foreign securities through various other investment vehicles including derivatives, which also involve other risks.

Currency Risk.  As long as the Fund holds a foreign security, its value will be affected by the value of the local currency relative to the U.S. dollar. When the Fund sells a foreign currency denominated security, its value may be worth less in U.S. dollars even if the security increases in value in its home country. U.S. dollar-denominated securities of foreign issuers may also be affected by currency risk, as the value of these securities may also be affected by changes in the issuer’s local currency.

Real Estate Securities Risk.  The Fund’s performance may be affected by the risks associated with investments in real estate-related companies. The value of real estate-related companies’ securities is sensitive to changes in real estate values and rental income, property taxes, interest rates, tax and regulatory requirements, supply and demand, and the management skill and creditworthiness of the company. Investments in real estate investment trusts (“REITs”) involve the same risks as other real estate investments. In addition, a REIT could fail to qualify for tax-free pass-through of its income under the Internal Revenue Code or fail to maintain its exemption from registration under the Investment Company Act of 1940, as amended, which could produce adverse economic consequences for the REIT and its investors, including the Fund.

Derivatives Risk.  Derivatives can be highly volatile and involve risks in addition to the risks of the underlying referenced securities. Gains or losses from a derivative investment can be substantially greater than the derivative’s original cost, and can therefore involve leverage. Leverage may cause the Fund to be more volatile than if it had not used leverage. Derivatives can be complex instruments and may involve analysis that differs from that required for other investment types used by the Fund. If the value of a derivative does not correlate well with the particular market or other asset class to which the derivative is intended to provide exposure, the derivative may not produce the anticipated result. Derivatives can also reduce the opportunity for gain or result in losses by offsetting positive returns in other investments. Derivatives can be less liquid than other types of investments and entail the risk that the counterparty will default on its payment obligations. If the counterparty to a derivative transaction defaults, the Fund would risk the loss of the net amount of the payments that it contractually is entitled to receive. To the extent the Fund enters into short derivative positions, the Fund may be exposed to risks similar to those associated with short sales, including the risk that the Fund’s losses are theoretically unlimited. In addition, to the extent that the Fund uses forward currency contracts, there is a risk that unanticipated changes in currency prices may negatively impact the Fund’s performance, among other things.

Allocation Risk.  The Fund’s ability to achieve its investment objective depends largely upon the allocation of assets among the equity and fixed asset categories. You could lose money on your investment in the Fund as a result of these allocations. Portfolio management may favor an asset category that underperforms relative to other asset categories. For example, the Fund may be overweighted in fixed-income securities when the stock market is rising and the fixed-income market is falling. Additionally, periodic rebalancing of Fund assets among asset categories may result in increased transaction costs, which may have a negative effect on the Fund’s performance.

Portfolio Turnover Risk.  Increased portfolio turnover may result in higher costs, which may have a negative effect on the Fund’s performance. In addition, higher portfolio turnover may result in the acceleration of capital gains and the recognition of greater levels of short-term capital gains, which are taxed at ordinary federal income tax rates when distributed to shareholders.

Management Risk.  The Fund is an actively managed investment portfolio and is therefore subject to the risk that the investment strategies employed for the Fund may fail to produce the intended results. The Fund may underperform its benchmark index or other mutual funds with similar investment objectives.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Please retain this Supplement with your records.