Does 30% Off Plus an Extra 10% Equal 40% Off?

Why Stacked Discounts Don't Add Up

When a retailer takes 30% off a price and then applies an extra 10% coupon, many shoppers expect the total to be 40% off. It feels logical — but the math doesn't work that way. The second discount applies to the already-reduced price, not the original. That smaller base means the extra 10% saves you less in dollar terms than 10% of the original would have.

The correct way to combine two discounts is to multiply the multipliers:

• 30% off → keep 70% → multiplier 0.70
• Extra 10% off → keep 90% of what's left → multiplier 0.90
• Combined: 0.70 × 0.90 = 0.63 → you pay 63%, save 37%

The order of the two discounts does not change the final result — 10% then 30% gives the same 37% total. But the total is always less than the simple sum (40%), because you're taking the second percentage off a smaller number.

Worked Example: $100 Item, 30% Off Then Extra 10%

Let's walk through a real shopping scenario step by step:

• Original price: $100
• After 30% off: $100 × 0.70 = $70
• After extra 10% off $70: $70 × 0.90 = $63
• Total saved: $100 − $63 = $37
• Effective discount: 37%, not 40%

That $3 difference (between the expected $60 and the actual $63 final price) happens because the extra 10% applies only to the post-sale $70, saving $7 — not 10% of the full $100 ($10).

The gap widens as the discounts get bigger, so it pays to check. A "50% off plus an extra 30%" promotion sounds like 80% off, but it is really 0.50 × 0.70 = 0.35, meaning you pay 35% and save 65% — a full 15 percentage points short of the 80% your gut assumed. On a $100 item that is the difference between paying $20 and paying $35. Whenever a sign advertises two stacked percentages, treat the headline number as marketing and run the multiplication before you decide the deal is as good as it looks.

The App's Stacked Discount Feature

This is exactly the scenario shown in screenshot 01: an item originally priced at $120, with 50% off first and then an extra 20% off stacked on top.

• After 50%: $120 × 0.50 = $60
• After extra 20%: $60 × 0.80 = $48
• Total saved: $72 (60% effective discount)

Discount Calculator: % Off has a dedicated Extra Discount field on the main calculator screen. Enter the original price, the first discount, and the extra discount — the app handles the multiplication correctly and shows you the final price, total savings, and effective percent off all at once. No chance of accidentally adding the percentages together. This is especially useful for coupon-on-sale situations where a store sale already reduced the price and your coupon takes another chunk off at the register.