Is backtesting a portfolio free?

Yes — you can backtest any mix of stocks and ETFs here for free, with no account, using 30+ years of split-adjusted prices and reinvested dividends.

How far back should I backtest?

As far as your holdings have data, and far enough to include at least one major downturn (2008 and 2020 are the key stress tests). A window with no bear market hides your true downside.

Does backtesting predict future returns?

No. It estimates how a strategy behaved historically. It's most useful for understanding risk and comparing strategies, not for forecasting.

How to Backtest a Portfolio: A Free, Step-by-Step Guide

7 min read · Updated 2026-06-15

Backtesting applies a portfolio's allocation to historical market data to estimate how it would have performed — its returns, the bumps along the way, and how deep the losses got. Done honestly, it turns “I think this mix is fine” into “here's exactly what this mix would have lived through.”

This guide walks through how to backtest a portfolio for free, how to read each result, and the traps that make a backtest look better than reality. You don't need a finance background or an account to follow along.

Run a free backtest →

What you need before you start

A backtest needs four simple inputs. Each one changes the result, so it's worth being deliberate:

•Tickers — the stocks or ETFs you hold (e.g. VTI, BND, or individual names).
•Target weights — the percentage of the portfolio in each holding. They should sum to 100%.
•A date range — the longer the better, because it has to include real downturns to be meaningful.
•A benchmark — usually a broad index (like the S&P 500) so you can see whether your mix actually beat “just buy the market.”

Step by step

1. Enter your holdings and weights. 2. Pick a start date that includes at least one bear market (2008 and 2020 are the useful stress points). 3. Choose a benchmark. 4. Run it. In a few seconds you get a full return-and-risk picture instead of a single number.

If you just want to see how it works, load a ready-made example first, then swap in your own tickers.

How to read the results

A good backtest reports more than “how much did it make.” The metrics that matter most for a real investor:

•CAGR (compound annual growth rate) — the smoothed yearly return. This is the headline growth number.
•Volatility — how much the returns bounced around. Higher means a rougher ride.
•Maximum drawdown — the worst peak-to-trough loss. This is the number that tells you whether you'd actually have held on.
•Sharpe & Sortino ratios — return earned per unit of risk. They let you compare two portfolios fairly, not just by raw return.
•Beta & alpha vs the benchmark — how much of your result came from simply moving with the market, and how much was genuine outperformance.

The mistakes that make a backtest lie

Most backtests flatter the portfolio. Watch for these:

•Overfitting — tweaking the mix until it looks perfect on past data. A portfolio tuned to ace history rarely repeats it.
•Too short a window — a backtest that starts in 2010 never saw 2008. If it didn't include a crash, you don't know the real downside.
•Ignoring dividends — price-only returns understate total return badly. Always reinvest dividends.
•Ignoring fees and taxes — small drags compound into large gaps over decades.
•Survivorship bias — testing only companies that still exist today quietly deletes the failures.

What a backtest can and can't tell you

A backtest is a study of the past, not a forecast. It's excellent for understanding risk — how deep the losses got, how long recovery took, whether two holdings move together — and for comparing strategies on a level field. It cannot predict future returns, and real markets have shocks no historical sample fully captures.

Use it to build conviction you can hold through a downturn, not to chase the mix with the prettiest past.

Try it yourself

Backtest PortfolioTest any mix of stocks & ETFs on decades of real data.Open tool →Stress TestReplay 2008, 2020, and 2022 against your exact holdings.Open tool →Asset Class BacktestBacktest by asset class instead of individual tickers.Open tool →

FAQ

Is backtesting a portfolio free?: Yes — you can backtest any mix of stocks and ETFs here for free, with no account, using 30+ years of split-adjusted prices and reinvested dividends.
How far back should I backtest?: As far as your holdings have data, and far enough to include at least one major downturn (2008 and 2020 are the key stress tests). A window with no bear market hides your true downside.
Does backtesting predict future returns?: No. It estimates how a strategy behaved historically. It's most useful for understanding risk and comparing strategies, not for forecasting.

Key terms in this guide

Plain-English definitions in the Learning Hub.

CAGR (Compound Annual Growth Rate) →Volatility (annualized standard deviation) →Maximum drawdown →Sharpe ratio →Beta →

Stop guessing — run the numbers on your own portfolio, free.