Indicator · Bollinger Bands
Bollinger Bands Backtester
Bollinger Bands get used for two opposite strategies — fade the touch, or ride the break — and both have devotees who are certain. They can't both be right on the same instrument and timeframe, and a few hundred logged touches will tell you which one your market pays for.
What the bands are measuring
A moving average, plus and minus a multiple of the standard deviation of price over the same window. CRTLAB defaults to 20 and 2 — the original settings — with both editable. Because the band width is the volatility, the bands narrow when the market goes quiet and flare when it moves. That is the entire mechanism, and every Bollinger strategy is a bet on what happens next at one of those two extremes.
The squeeze, and the honest way to test it
"The squeeze precedes the expansion" is true and nearly useless on its own, because it says nothing about direction. Test it as a two-part rule: log every squeeze by your own width threshold, then record which way price broke and whether the first break held. The proportion of squeezes that break, reverse, and break again the other way is the number that decides whether this is tradeable for you.
Fading the outer band is the opposite test, and the one where a replay matters most: in a strong trend price walks the upper band for twenty candles, and every single fade is a loss. Scrolling a chart you skip past those; stepping candle by candle you have to sit in them, which is exactly the experience the backtest is meant to give you.
Frequently asked questions
Can I change the period and standard deviation?
Yes, both from the chart legend — 20 and 2 by default, and the bands redraw across the whole replay immediately when you change either.
Do the bands use a simple or exponential average as the middle line?
The classic simple moving average, which is what makes the standard-deviation calculation match the original definition.
Is it free to backtest Bollinger Bands?
Yes — free on all 21 free markets for the most recent two weeks of data, with no account. Pro extends the same test across the full history.
Open gold with Bollinger Bands on
One click — 15-minute XAUUSD, bands plotted, replaying candle by candle.
Open the chart →