How it's calculated
final = price × (1 − d₁) × (1 − d₂) × …
price = original price, d = each discount as a fraction (e.g. 20% = 0.20); discounts stack sequentially. Savings = price − final.
Common questions
Do two discounts add together?
No, and this catches people out. 20% off then another 10% off is 28% off, not 30% — the second cut comes off the already-reduced price.
How do I work out percent off?
Multiply the price by the discount as a decimal. $80 at 25% off is 80 × 0.25 = $20 off, leaving $60.
Does it add sales tax?
If you switch tax on and enter the rate, it adds tax after the discounts, the way a checkout does.