Take it off, and see what's really left

Take the old value, subtract the new one, divide by the old value, then multiply by 100. From 240 down to 204: (240 − 204) ÷ 240 × 100 = 15%. Dividing by the new value is the usual mistake and gives an inflated answer.

No, and the shop is counting on you thinking it is. The second discount comes off the already-reduced price, so you pay 0.70 × 0.80 = 0.56 — that's 56% of the original, meaning 44% off, not 50%. The gap widens with bigger discounts: 50% then 50% is 75% off, not 100%. The "Stacked discounts" tab shows both steps.

Divide, don't add the percentage back. A £204 item at 15% off started at 204 ÷ 0.85 = £240. Adding 15% to 204 would give 234.60, which is wrong, because the 15% was calculated from the bigger number.

The fall is measured against the original amount; the recovery is measured against the smaller amount that's left. A 20% fall needs a 25% rise, a 50% fall needs 100%, and a 90% fall needs 900%. Formula: D ÷ (100 − D) × 100. The Recovery tool works it out for any drop.

Not if it can't go below zero — a 100% decrease removes everything there is. You'll only see figures beyond 100% where negative values are meaningful, such as a profit swinging into a loss. In that case the percentage is describing a change of direction, not just a reduction.

Far more than the discount percentage suggests. On an item costing 60 and selling at 100, your margin is 40. Knock 10% off the price and you sell at 90 — the margin drops to 30, a 25% cut in profit from a 10% cut in price. Thin margins amplify this: at a 20% margin, a 10% discount halves your profit.