Methodology

Data source

Stock and ETF prices come from IEX Historical Data, the free historical files of IEX (Investors Exchange). Each month-end price is the last regular-session trade on IEX that day; where there was none, it is that day's last odd-lot trade on IEX, or else the previous month-end's price. Histories start in December 2016 at the earliest. The exchange rates behind the currency selector come from the European Central Bank and the Federal Reserve, as described under currency conversion below.

Adjustment convention

Price return: adjusted for stock splits, dividends not included. Prices are split-adjusted automatically; a ticker whose history we could not adjust with confidence starts later or is not shown.

Time resolution

Tables, year scenarios and the calculator use month-end closes. A scenario "in year Y" invests at the December Y−1 month-end close and values the position at the latest close. A date entered in the calculator resolves to the close at the end of its month, and the result says which close it used.

Dollar-cost averaging

A monthly contribution of $X adds $X at every month-end close between the start and end dates, on top of the starting amount, and buys fractional shares at that close. Contributions count in full toward the invested total.

Currency conversion

An amount in another currency is converted into US dollars at the buy date's exchange rate, grown in dollars, and converted back at the sell date's rate, so the result includes the currency move. Each month uses one rate: the last rate published in that month, or the latest rate for a month still in progress. From January 1999 the rates are the European Central Bank's euro foreign exchange reference rates (from April 2005 for the Chinese yuan and January 2009 for the Indian rupee, when the ECB added them), which this site converts into US dollars per unit of each currency by dividing the ECB's US dollar rate by its rate for that currency. Earlier months use the Federal Reserve Board's H.10 rates, the noon buying rates in New York, which go back to 1971 for most of the currencies offered. Both banks publish one rate per business day, so these can differ slightly from a market's closing rate. A buy date before a currency's first rate uses that first rate, and the result says so.

Benchmark comparisons

"Beat the S&P 500" comparisons invest $1,000 in the ticker and $1,000 in an S&P 500 index fund over the same months, both at month-end closes, and compare the results. The fund figure includes reinvested dividends; the stock figure does not, so the comparison favors the fund.

The comparison fund is the TSP C Fund, an S&P 500 index fund, with dividends reinvested. The C Fund is the Thrift Savings Plan's S&P 500 index fund for federal employees and members of the uniformed services, and the Federal Retirement Thrift Investment Board publishes its monthly returns at tsp.gov. The fund began on January 29, 1988, so comparisons start from the January 1988 month-end, and a purchase before then has no market comparison. Each month's return is published after the month ends, so a comparison runs to the latest month the fund has reported, and the ticker and the fund are both valued at that same month-end. Every per-year page on this site is for a year after the fund began. A per-year page shows a comparison once both the ticker and the fund have a completed month after the page's purchase, so the current year's pages have none in January and early February, until the fund reports January.

Correction: until 31 August 2026 the comparison used the price index for the whole span, against tickers carried with dividends reinvested. That understated the market alternative by roughly 9% for a 2020 entry, 26% for 2010, 38% for 2000 and 52% for 1990. This page used to call that gap slight. The figures on the site have been recomputed.

Real-thing equivalents

The result card translates dollar values into real things (Big Macs, troy ounces of gold and silver, gallons of gas, hours of federal-minimum-wage work, the median American house) at the prices of the dates involved. Each equivalent uses the most recent monthly observation at or before your date (last observation carried forward, never interpolated, never extrapolated before a series begins), so "it was 248 Big Macs" prices the burger in your buy month. Gold and silver are world prices in US dollars; the other anchors are US national figures. Treat the equivalents as illustrations: nobody is valuing your portfolio in burgers.

The house yardstick has a whole calculator behind it: House Regrets prices the house you didn't buy, metro by metro, with the mortgage leverage and the rent you paid instead.

Limits

Prices are the last regular-session trade on IEX (Investors Exchange) each day, which can differ slightly from the official close. No taxes, trading fees or spreads are modeled, so real accounts would keep less. Tables use one close per month, so they miss the highs and lows inside a month.

Attribution

Market data: IEX Historical Data. This site is not affiliated with, or endorsed by, any data provider. Ticker and year pages state the date of the last IEX trade they use. Prices are end-of-day; the site shows no real-time quotes.

Exchange rates: euro foreign exchange reference rates, source: European Central Bank (ecb.europa.eu), converted by this site into US dollars per unit of each currency, one rate per month; and H.10 foreign exchange rates, source: Board of Governors of the Federal Reserve System (federalreserve.gov), public domain.

Real-thing equivalents: Big Mac prices from The Economist's Big Mac Index dataset (CC BY 4.0); gold and silver monthly prices from World Bank Commodity Price Data ("The Pink Sheet", CC BY 4.0); median home sales prices (US Census Bureau and HUD, via FRED), average gasoline prices (US Bureau of Labor Statistics), and the federal minimum wage schedule (US Department of Labor) are US government data in the public domain.

Market comparisons: monthly returns of the TSP C Fund, published by the Federal Retirement Thrift Investment Board at tsp.gov. This site is not affiliated with, or endorsed by, the Thrift Savings Plan.