What Is Walk-Forward Testing

Walk-forward in five lines

Walk-forward testing is out-of-sample testing done over and over, stepping through the tape. Each step fits the rule's numbers on a window of bars, tests them on the slice that comes next, and steps forward to do it again. What it gives is a chain of out-of-sample slices joined end to end, which is the only result worth reading, and what it shows is whether refitting keeps up with the bars, and how often the numbers change. In the example, the euro's best buy-and-sell hours were refitted every week on the previous four weeks and tested on the week that followed, 23 times through 2026: 52.1 pips in all, where a pip is the fourth decimal place of the price, with 13 of the 23 weeks up.

The windows step along the tape

Picture the windows stepping along the tape. Each grey bar is a fit window, four weeks of bars on which the rule's numbers are chosen; the gold slice after it is the test week, met once with those numbers fixed. Then everything steps one week to the right and it happens again. The grey windows overlap heavily, which is fine, because they are only where the choosing happens; the gold slices never overlap, and joined end to end they are the walk-forward result, a run of bars none of which the rule in force at the time had seen.

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