Stacking Discounts Calculator

Why 10% Off + 20% Off ≠ 30% Off

This is one of the most common math misconceptions in shopping. When a store offers two sequential discounts, the second discount applies to the already-reduced price, not the original price.

Example: $100 with 10% off, then 20% off:

Step 1: $100 × 0.90 = $90.00
Step 2: $90 × 0.80 = $72.00

A single 30% discount would give $70.00 — that's $2 less. The difference grows with larger numbers: on a $1,000 purchase, the gap is $20.

The Order Doesn't Matter

Good news: whether you apply 10% first then 20%, or 20% first then 10%, the final price is identical. Multiplication is commutative: 0.90 × 0.80 = 0.80 × 0.90.

Real-World Stacking Scenarios

Store sale + coupon: A store runs a 15% off sale and you have a 10% off coupon. Real discount = 23.5%, not 25%.

Employee discount + member discount: 10% employee + 10% member = 19% total, not 20%.

Triple stack (rare): Three 10% discounts stack to 27.1% off, not 30%.