Forex chart replay: how to practise on past price data

Replay, manual testing and backtesting are not the same thing

The three get used interchangeably, but they differ in who makes the trading decision. Chart replay is the mechanism: past candles advanced one at a time. Manual testing is what you do with it — trying your own judgement against a market whose outcome you cannot see. Backtesting fixes the rules in advance and lets a machine compute every trade at once.

So in replay you are the one deciding, which is what makes it practice for discretionary trading. In a backtest the rule decides, and what you measure is whether that rule held up. If you cannot yet write your method down as rules, replay gets you moving sooner.

What the routine looks like

Four things make it a test rather than a scroll. Skip the third and all you keep is the memory of having guessed right.

1. Pick a pair and a timeframe
2. Start somewhere you do not already know the outcome
3. Advance one bar at a time and actually record each entry and exit
4. At the end, read the win rate, the P&L and the average win

Which pair to practise on

How far a pair travels in a day varies widely. GBP/JPY averages 153.9 pips a day and NZD/USD averages 63.5 pips (2016–2025, 2,595 trading days). Trade the same size on both and the first swings your balance about 2.4× as far as the second.

Early on the narrower pair is the better teacher. A sense of "this much drawdown is normal" built on GBP/JPY does not transfer to NZD/USD. The per-pair figures are on the volatility tables.

Which hours to choose

USD/JPY moves most in the 14:00 UTC hour, which alone averages 27.8 pips (2016–2025) — the stretch where London and New York overlap.

For practice the two kinds of hour teach different things. Busy hours generate decisions quickly, so you accumulate trades. Quiet hours are where you practise waiting. Testing only one of them leaves half the job undone.

How many trades before the number means anything

One session's win rate is not the method's win rate. Eleven wins out of twenty reads as 55%, and a single trade going the other way makes it 50%. Repeating the same rules across several sessions and looking at the spread tells you more than any one figure.

Formiq's daily practice picks the pair and the period for you and ends after 20 trades. Fixing the size of a session is what makes two sessions comparable.

Where it usually goes wrong

When replay practice stops paying off, it is normally one of these.

1. Peeking ahead and rewinding — a decision made after seeing the answer is not practice
2. Keeping no record, so by next week only the impression survives, not the win rate
3. Changing the rules every run, which makes it impossible to tell what worked
4. Replaying the same favourable stretch, when the value is in periods that behave differently