Why do the numbers change when I change the date range?

Almost every statistic on this site is computed over the date range you have selected, not over the strategy's full history. Move the range and the numbers move with it. This is intended, but a few of the behaviors surprise people, and one of them can be genuinely misleading if you do not know about it.

The general rule

CAGR, Max Drawdown, Ulcer Index, UPI, Sharpe, Sortino, standard deviation, alpha, beta, and the withdrawal rates are all window-scoped. Each is recomputed from the months inside your selection and nothing outside it.

So a strategy showing a 14% CAGR over its full history and 9% over the last five years is not contradicting itself. Those are two different measurements of two different periods.

The drawdown clock restarts

This one deserves particular attention.

Max Drawdown measures the decline from a running high-water mark. That high-water mark resets to the first month of your selected range. The calculation has no memory of anything before your window opens.

If your range begins partway into a decline, the true peak that preceded it is invisible, and the drawdown is measured from an already-depressed value. A range that starts at a market bottom will make nearly any strategy look serene, because the calculation never sees the fall that created the bottom.

The practical consequence: when you are trying to understand risk rather than study a particular episode, use the full available range. Narrow windows are for examining a specific period, not for judging how much pain a strategy can inflict.

The risk-free rate changes with the window

Sharpe, Sortino, and UPI all measure return above cash, and DMS uses the actual cash return over your selected period rather than a fixed assumption.

Cash yielded close to 10% in the early 1980s and nearly nothing through the 2010s. A window covering the first is holding the strategy to a far higher standard than a window covering the second. Risk-adjusted figures from very different eras are not directly comparable, even for the same strategy.

Some things do not change with the window

A few figures are computed over the strategy's entire history regardless of your selection:

• The LT Gains percentage applied by the Taxable Account toggle is always full-history. The Tax Profile panel showing you an LT Gains percentage is window-scoped, so the two can display different numbers. Narrowing the range changes the panel but not the tax actually being charged.
• Strategy inception dates and coverage are properties of the data, not of your selection.

Short windows are noisy

A statistic computed over 24 months is a much weaker claim than the same statistic over 300 months, and the site does not visually distinguish between them.

Some measures refuse to compute below a minimum. The withdrawal rates require ten years. The Tax Profile requires twelve months of allocation data. Most others will happily return a number from a very short window, and that number deserves proportionally less trust.

Comparing strategies fairly

When comparing two strategies, make sure the window covers a period both actually lived through. A strategy that launched in 2015 compared against one going back to 1979 over the maximum range is not a comparison of strategies. It is a comparison of eras.

The comparison views handle the common cases by aligning the period, but it is worth checking the start dates yourself when a result looks surprising.

Quick checklist when a number looks wrong

1. What date range is selected?
2. Does that range start in the middle of a decline?
3. Are the Inflation Adjusted, Trading Friction, or Taxable Account toggles on?
4. Does the window cover a period both strategies existed for?
5. Is the window long enough for the statistic to mean anything?

Most surprises resolve at one of those five.