How to calculate percent off: the simple math behind sale prices

'30% off' sounds obvious until you're standing in a store. Here's the exact math, plus a mental trick so fast you'll do it in your head.

The one formula you need

To find a sale price: multiply the original price by (1 − discount). A $80 jacket at 30% off costs 80 × 0.70 = $56. The 0.70 is what's left after removing 30% — this works for any percent and any price.

The mental-math trick

10% is just the price with the decimal moved one step left: $80 → $8. So 30% = 3 × $8 = $24 off. For 15%, take 10% plus half of it again ($8 + $4 = $12). No calculator required — though our percent off calculator handles the fiddly cases.

Why double discounts are traps

'50% + 20%' is not 70% off. The second discount applies to the already-discounted price: 80 × 0.5 × 0.8 = $32 — that's 60% off in total, not 70%. Check any stacked deal with our percentage calculator before you celebrate.

Percent off vs. percent of

Percent off subtracts (you pay the remainder); percent of is the share itself. 30% off $80 = pay $56. 30% of $80 = $24. Mixing these two up is the most common money mistake in retail math.