Percent Off Calculator · Practical guide
20 Percent Off Plus an Extra 10 Percent Off
Stacked discounts multiply instead of adding, so 'extra 10% off' always saves you less than the sign suggests.
At a glance
The Short Answer: It Is 28% Off, Not 30%
When a store advertises 20% off plus an extra 10% off, the second percentage applies to the already-reduced price. On a $100 item: the first discount takes it to $100 × 0.8 = $80, and the extra 10% removes $8, leaving $72. Your total saving is $28 on $100 — an effective discount of 28%, not the 30% you would get by adding the two numbers.
Interactive tool
Percent Off Calculator
Enter your own values, then compare the result with the examples below.
Discount Breakdown
The Stacked Discount Formula
Successive discounts multiply: Final price = Original × (1 − D1 ÷ 100) × (1 − D2 ÷ 100). The combined effective rate is 1 − (1 − D1 ÷ 100) × (1 − D2 ÷ 100). For 20% and 10%: 1 − 0.8 × 0.9 = 1 − 0.72 = 0.28, or 28%.
Common Stacked Combinations on a $100 Item
| Discounts | Final Price | Effective Savings |
|---|---|---|
| 10% + 10% | $81.00 | 19% |
| 20% + 10% | $72.00 | 28% |
| 25% + 15% | $63.75 | 36.25% |
| 30% + 20% | $56.00 | 44% |
| 40% + 10% | $54.00 | 46% |
| 50% + 20% | $40.00 | 60% |
The gap between the advertised numbers and the true discount grows as the percentages grow: "50% off plus an extra 50% off" still leaves $25 of a $100 item — a 75% effective discount, not a free item. Enter both percentages in the calculator above to see the price after each step, plus the effective savings rate.
Frequently Asked Questions
Why isn't 20% off plus 10% off equal to 30% off?
Because the extra 10% comes off the reduced $80 price, not the original $100. Ten percent of $80 is $8, so you save $28 total instead of $30.
Does the order of the two discounts matter?
No. Multiplication is commutative, so 20% then 10% gives the same final price as 10% then 20%.
Is 50% off plus an extra 50% off free?
No. The first discount halves the price and the second halves it again, leaving 25% of the original — a $100 item still costs $25.
Can I stack a dollar-off coupon on top?
Usually yes. Subtract the coupon after the percentage discounts, then apply sales tax to the final amount.