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Institutional | Vanguard Extended Duration Treasury Index Fund

Fund Summary

Investment Objective

The Fund seeks to track the performance of an index of extended-duration zero- coupon U.S. Treasury securities.

Fees and Expenses

The following table describes the fees and expenses you may pay if you buy and hold Institutional Shares or Institutional Plus Shares of the Fund.

Shareholder Fees (Fees paid directly from your investment)

Shareholder Fees - Institutional - Vanguard Extended Duration Treasury Index Fund	Institutional Shares	Institutional Plus Shares
Sales Charge (Load) Imposed on Purchases	none	none
Purchase Fee	0.50%	0.50%
Sales Charge (Load) Imposed on Reinvested Dividends	none	none
Redemption Fee	none	none

Annual Fund Operating Expenses (Expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses - Institutional - Vanguard Extended Duration Treasury Index Fund		Institutional Shares	Institutional Plus Shares
Management Fees		0.06%	0.04%
12b-1 Distribution Fee		none	none
Other Expenses	[1]	none	none
Total Annual Fund Operating Expenses		0.06%	0.04%

Examples

The following examples are intended to help you compare the cost of investing in the Fund's Institutional Shares or Institutional Plus Shares with the cost of investing in other mutual funds. They illustrate the hypothetical expenses that you would incur over various periods if you were to invest $10,000 in the Fund's shares. These examples assume that the shares provide a return of 5% each year and that total annual fund operating expenses remain as stated in the preceding table. You would incur these hypothetical expenses whether or not you were to redeem your investment at the end of the given period. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example - Institutional - Vanguard Extended Duration Treasury Index Fund - USD ($)	1 Year	3 Years	5 Years	10 Years
Institutional Shares	6	19	34	77
Institutional Plus Shares	4	13	23	51

Portfolio Turnover

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in more taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the previous expense examples, reduce the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 20% of the average value of its portfolio.

Principal Investment Strategies

The Fund employs an indexing investment approach designed to track the performance of the Bloomberg Barclays U.S. Treasury STRIPS 20–30 Year Equal Par Bond Index. This Index includes zero-coupon U.S. Treasury securities (Treasury STRIPS), which are backed by the full faith and credit of the U.S. government, with maturities ranging from 20 to 30 years. A Treasury STRIP represents a single coupon payment, or a single principal payment, from a U.S. Treasury security that has been "stripped" into separately tradable components.

The Fund invests by sampling the Index, meaning that it holds a range of securities that, in the aggregate, approximates the full Index in terms of key risk factors, including duration, cash flow, and other characteristics. All of the Fund's investments will be selected through the sampling process, and under normal circumstances, at least 80% of the Fund's assets will be invested in U.S. Treasury securities held in the Index. The Fund maintains a dollar-weighted average maturity consistent with that of the Index, which generally ranges between 20 and 30 years. As of August 31, 2019, the dollar-weighted average maturity of the Index was 24.6 years.

Principal Risks

An investment in the Fund could lose money over short or long periods of time. You should expect the Fund's share price and total return to fluctuate within a wide range. The Fund is subject to the following risks, which could affect the Fund's performance:

• Interest rate risk, which is the chance that bond prices overall will decline because of rising interest rates. The prices of long-term bonds, such as those held by the Fund, are much more sensitive to interest rate changes than are the prices of short-term bonds. Interest rate risk is expected to be very high for the Fund because it invests primarily in zero-coupon long-term bonds, which have prices that are even more sensitive to interest rate changes than are coupon-bearing bonds of similar maturity. Because the Fund invests primarily in Treasury STRIPS with maturities ranging from 20 to 30 years, rising interest rates may cause the value of the Fund's investments to decline significantly.

• Index sampling risk, which is the chance that the securities selected for the Fund, in the aggregate, will not provide investment performance matching that of the Fund's target index. Index sampling risk for the Fund is expected to be low.

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

Annual Total Returns

The following bar chart and table are intended to help you understand the risks of investing in the Fund. The bar chart shows how the performance of the Fund's Institutional Shares (including annual fund operating expenses but excluding shareholder fees) has varied from one calendar year to another over the periods shown. If applicable shareholder fees were reflected, returns would be less than those shown in the bar chart. The table shows how the average annual total returns of the share classes presented (including annual fund operating expenses and any applicable shareholder fees) compare with those of the Fund's target index, which has investment characteristics similar to those of the Fund. Keep in mind that the Fund's past performance (before and after taxes) does not indicate how the Fund will perform in the future. Updated performance information is available on our website at vanguard.com/performance or by calling Vanguard toll-free at 800-662-7447.

Annual Total Returns — Vanguard Extended Duration Treasury Index Fund Institutional Shares

During the periods shown in the bar chart, the highest return for a calendar quarter was 52.05% (quarter ended September 30, 2011), and the lowest return for a quarter was –20.01% (quarter ended March 31, 2009).

Average Annual Total Returns for Periods Ended December 31, 2018

Average Annual Total Returns - Institutional - Vanguard Extended Duration Treasury Index Fund - Institutional Shares	1 Year	5 Years	10 Years
Before Taxes	(3.98%)	9.03%	3.20%
Return After Taxes on Distributions	(5.14%)	7.45%	1.13%
Return After Taxes on Distributions and Sale of Fund Shares	(2.38%)	6.44%	1.56%
Bloomberg Barclays U.S. Treasury STRIPS 20-30 Year Equal Par Bond Index (reflects no deduction for fees, expenses, or taxes)	(4.16%)	8.91%	3.41%

Average Annual Total Returns - Institutional - Vanguard Extended Duration Treasury Index Fund - Institutional Plus Shares	1 Year	5 Years	Since Inception	Inception Date
Before Taxes	(3.97%)	9.05%	7.61%	Aug. 28, 2013
Bloomberg Barclays U.S. Treasury STRIPS 20-30 Year Equal Par Bond Index (reflects no deduction for fees, expenses, or taxes)	(4.16%)	8.91%	7.69%	Aug. 28, 2013

Actual after-tax returns depend on your tax situation and may differ from those shown in the preceding table. When after-tax returns are calculated, it is assumed that the shareholder was in the highest individual federal marginal income tax bracket at the time of each distribution of income or capital gains or upon redemption. State and local income taxes are not reflected in the calculations. Please note that after-tax returns are shown only for the Institutional Shares and may differ for each share class. After-tax returns are not relevant for a shareholder who holds fund shares in a tax- deferred account, such as an individual retirement account or a 401(k) plan. Also, figures captioned Return After Taxes on Distributions and Sale of Fund Shares may be higher than other figures for the same period if a capital loss occurs upon redemption and results in an assumed tax deduction for the shareholder.

[1] 0.00%

[1] The year-to-date return as of the most recent calendar quarter, which ended on September 30, 2019, was 27.38%.