Guide
Choosing Start and End Dates for a Backtest
The same ticker can look very different depending on the window you choose. Date choice is part of the result, so test more than one range to see how sensitive the story is.
Published: December 26, 2025 · Updated: December 26, 2025 · By FinToolSuite Editorial
Disclaimer
- Educational purposes only, not financial advice.
- Examples are illustrative and simplified.
- Past performance is not a reliable indicator of future results.
- Market returns can be negative.
- See the Privacy Policy for data handling details.
Open the Investment History Checker
Run one window, then shift dates to see how results change.
Quick answer
- Dates change what you include and exclude.
- Short windows can exaggerate good or bad luck.
- Use multiple windows to reduce cherry picking.
Why start and end dates matter
Markets move in cycles. Starting at a peak versus a dip changes returns and drawdowns. Ending right after a crash versus after a recovery tells a different story even with the same ticker.
Short vs medium vs long windows
- Short windows: can be noisy.
- Medium windows: often show one cycle.
- Long windows: show multiple cycles but include structural changes.
Quick illustrative examples
| Window | Start value | End value | Illustrative return | What changed |
|---|---|---|---|---|
| 1 year | 100 | 110 | 10% | Captures one short move |
| 5 years | 100 | 150 | 50% | Includes a dip and recovery |
| 10 years | 100 | 200 | 100% | Multiple cycles included |
Illustrative only; the same asset can show different answers because the path differs.
How to avoid cherry picking
- Run at least two to three windows.
- Include one window that starts before a major drop if possible.
- Include one longer window.
- Compare return and drawdown together.
See more pitfalls in common mistakes.
Step by step workflow in the tool
- Choose your ticker.
- Pick a baseline window you care about.
- Run it and save as a scenario.
- Move the start date earlier by a fixed amount and rerun.
- Move the end date later or earlier and rerun.
- Compare CAGR, total return, max drawdown, and yearly pattern.
You can also test lump sum versus contributions on the same dates; see lump sum vs DCA and check best and worst year explained.
Common date selection mistakes
- Choosing only a recent bull run.
- Choosing an unusually good or bad year.
- Comparing two tickers on different windows.
- Ignoring currency differences.
- Assuming the window predicts the future.
More pitfalls are listed in common mistakes.
Quick checklist
- [ ] Same dates when comparing two tickers
- [ ] At least two windows tested
- [ ] Return and drawdown read together
- [ ] Best and worst years reviewed
FAQ preview
How long should my window be?
Test short, medium, and long windows to see how sensitive results are.
Why does moving dates change CAGR a lot?
Different peaks and troughs are included when you shift dates.
Should I compare different tickers with the same dates?
Yes, that keeps the window consistent; just note currency differences.
What if the ticker has limited history?
Use the overlapping window and recognize shorter history can be noisy.
Where do I see best and worst years?
Check the best and worst year metrics and the yearly table in the tool.
Test multiple windows
Run one range, shift the dates, and export results to see how the story changes.