Stop loss calculator
Find your stop loss price three ways at once: a fixed percent below entry, a multiple of the stock's ATR (how much it normally moves in a day), or the price where you'd lose a set dollar amount.
Percent stop
$47.50
5% below entry · $2.50 (5.0%) below entry
ATR stop
$47.20
2 × ATR ($1.40) below entry · $2.80 (5.6%) below entry
Max-loss stop
$47.50
lose $100.00 on 40 shares · $2.50 (5.0%) below entry
For a long trade. Pick the stop that sits below a real support level, not just the one that feels comfortable, then size the trade with the position size calculator.
How it works
- 1Percent stop = entry × (1 − percent). Simple, but ignores how volatile the stock is.
- 2ATR stop = entry − ATR × multiple. A stop 1.5 to 2 ATR away sits outside normal daily noise. You can find ATR(14) on most charting sites.
- 3Max-loss stop = entry − (max loss ÷ shares). Useful when the share count is fixed; check that this price makes sense on the chart.
- 4The best stop is usually just below a real support level or swing low. Use these numbers as a check, not a replacement for the chart.
Questions people ask
How do I calculate a stop loss price?
For a percent stop, multiply the entry by (1 − percent). For an ATR stop, subtract a multiple (often 1.5–2) of the average true range from the entry. Then check the price sits below a sensible support level.
What percentage should a stop loss be?
There's no single right number. Many swing traders end up 3–8% below entry, but a volatile stock needs a wider stop than a calm one. That's why ATR stops adapt better than fixed percents.
What is an ATR stop loss?
A stop placed a multiple of the Average True Range below your entry. ATR measures a stock's typical daily movement, so the stop adapts to how volatile the stock is.
Let Boo plan the trade for you
Upload a screenshot of any chart or type a ticker. Boo reads it and hands you the entry, stop loss, target and position size in seconds. Your first full plan is free.