{"schemaVersion":"1.0","type":"BacktestEvidence","id":"https://formiq.jp/evidence/bollinger-band-period-settings/data.json","evidencePage":"https://formiq.jp/evidence/bollinger-band-period-settings","language":"en","article":{"title":"Bollinger Bands Period: Is 20 Really Best? 3,024 Settings Tested","url":"https://formiq.jp/blog/bollinger-band-period-settings","published":"2026-08-28","updated":"2026-08-30"},"author":{"name":"Yuichi Saiki","alternateName":"斉木勇一","url":"https://formiq.jp/about/yuichi-saiki"},"verified":"2026-08-30","question":"Is Bollinger period 20 optimal, and is there one bar count that works on every timeframe?","finding":"There was no universal bar count. Averaging seven breakout deviations across 2024 and 2025, period 50 led the 15-minute chart, period 20 the hourly chart and period 5 the four-hour chart — different counts that represent similar lookbacks of 12.5 to 20 hours. On hourly bars period 20 had the highest two-year mean at +1,562.7 pips with all seven deviations profitable in both years, but its seven-deviation mean was −211.0 pips in the first half of 2025 and only two deviations were profitable in both halves. Lengthening the period widened the mean half-width at 1σ from 12.79 pips at period 5 to 88.68 at period 200 and cut annual breakout trades from 934 to 46, yet the share of closes inside the bands stayed between 44.9% and 50.3% rather than rising with the period. Period 5 at 2σ is impossible in this implementation and recorded no trades in all 12 timeframe-and-window cells.","methodology":"Measured with Formiq's production backtester across three trading rules: long fade, short fade and close breakout. Fills use the signal bar's close. An opposite-side reversal may occur on the exit bar, while same-side re-entry waits for a later bar. No stop or target in the main grid.","scope":["USDJPY. Calendar 2025, calendar 2024, and the two halves of 2025","15-minute, hourly and four-hour bars; 24,903 M15 bars in 2025, 6,226 H1 and 1,610 H4","12 periods (5 to 200) x 7 deviations (0.5σ to 2σ) x 3 trading rules = 252 settings, on 3 timeframes and 4 windows: 3,024 runs","0.3 pip spread, 0.1 lots, zero slippage"],"keyResults":[{"label":"Leading period by two-year mean","value":"50 on M15, 20 on H1, 5 on H4 — 12.5 to 20 hours of elapsed time"},{"label":"Period 20 on hourly bars","value":"all seven deviations profitable in both years, +1,562.7 pip two-year mean, but −211.0 pips in the first half of 2025"},{"label":"Period 5 at 2σ","value":"arithmetically impossible; no trades in all 12 cells"}],"limitations":["One pair and two calendar years.","The best period changed by timeframe and cannot be assumed to transfer to another pair or to daily bars.","Selecting from 12 periods and seven deviations creates multiple-comparison uplift. The opposite year is a check, not untouched future data.","Period 5 and 2σ is impossible under this population-standard-deviation implementation. A sample deviation, or a calculation that excludes the current close, changes the boundary.","Touches use highs and lows; breakouts use closes.","An open position is closed at the final bar of each window, so the two half-year results do not add exactly to the calendar-year result."]}