Label

Element

Value

Prospectus [Line Items]

rr_ProspectusLineItems

Document Type

dei_DocumentType

497

Document Period End Date

dei_DocumentPeriodEndDate

Aug. 31, 2023

Entity Registrant Name

dei_EntityRegistrantName

First Trust Exchange-Traded Fund VIII

Entity Central Index Key

dei_EntityCentralIndexKey

0001667919

Entity Inv Company Type

dei_EntityInvCompanyType

N-1A

Amendment Flag

dei_AmendmentFlag

false

Document Creation Date

dei_DocumentCreationDate

Mar. 13, 2024

Document Effective Date

dei_DocumentEffectiveDate

Mar. 13, 2024

FT Vest Buffered Allocation Defensive ETF

Prospectus [Line Items]

rr_ProspectusLineItems

Supplement to Prospectus [Text Block]

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1. Notwithstanding anything to the contrary in the Fund’s prospectus, effective as of the date set forth above, the fourth paragraph through the eighth paragraph (not counting sub-headers) set forth in the section entitled “Principal Investment Strategies” shall be deleted in their entirety and replaced with the following:

The universe of Underlying ETFs from which the Sub-Advisor selects the Fund’s portfolio consists of four different types of “target outcome” ETFs, as described below.

FT Vest U.S. Equity Buffer ETFs

The series of FT Vest U.S. Equity Buffer ETFs seek to provide investors with returns that match the price return of SPY up to a predetermined upside cap (before fees and expenses), while providing a buffer (before fees and expenses) against the first 10% of SPY losses, over a defined one year period.

FT Vest U.S. Equity Deep Buffer ETFs

The series of FT Vest U.S. Equity Deep Buffer ETFs seek to provide investors with returns that match the price return of SPY up to a predetermined upside cap (before fees and expenses), while providing a buffer (before fees and expenses) against SPY losses between -5% and -30%, over a defined one year period.

FT Vest U.S. Equity Enhance & Moderate Buffer ETFs

The series of FT Vest U.S. Equity Enhance & Moderate Buffer ETFs seek to provide investors with returns of approximately twice any positive price return of SPY up to a predetermined upside cap (before fees and expenses), while providing a buffer (before fees and expenses) against the first 15% of SPY losses, over a defined one year period.

FT Vest U.S. Equity Moderate Buffer ETFs

The series of FT Vest U.S. Equity Moderate Buffer ETFs seek to provide investors with returns that match the price return of SPY up to a predetermined upside cap (before fees and expenses), while providing a buffer (before fees and expenses) against the first 15% of SPY losses, over a defined one year period.

In allocating the Fund’s portfolio among the universe of possible Underlying ETFs described above, the Fund’s Sub-Advisor evaluates various factors, including, but not limited to, the current price of SPY, the NAV of each Underlying ETF, the number of days left in each Target Outcome Period, implied market volatility, the price sensitivity of the underlying FLEX Options to price movements of SPY, and the remaining upside potential (cap) and remaining downside protection (buffer) offered by each Underlying ETF relative to the others in the universe. From this evaluation, the Sub-Advisor selects 5-7 Underlying ETFs for the Fund’s portfolio that it believes have the greatest potential for downside protection based on current market conditions, while still providing a level of upside growth participation. The weighting of each Underlying ETF will be determined by the Sub-Advisor using the factors listed above. The Fund’s portfolio will be evaluated on a quarterly basis.