Stacked Discounts: Why 30% + 10% Isn't 40% Off
"30% off, plus an extra 10% at checkout" reads like 40% off total. It isn't. The second discount doesn't apply to the original price — it applies to whatever's left after the first one, and that difference adds up to real money on anything beyond a small purchase.
What's actually happening
Percentages stack multiplicatively, not by simple addition, because each one is calculated against a different starting point. Take a $100 item at 30% off: that brings it to $70. A second discount of 10% doesn't apply to the original $100 — it applies to the $70 that's already been discounted, taking off another $7 rather than another $10. The final price is $63, not the $60 that "40% off" would suggest.
That's a $3 difference on a $100 item — small in isolation, but it scales directly with price. On a $1,000 purchase, the same stacked discounts come out to $30 more than the "just add the percentages" shortcut implies. The bigger the price tag, the more that gap actually costs you if you're budgeting off the wrong number.
Why retailers structure it this way
This isn't a trick exactly — it's just how sequential percentage discounts mathematically have to work once you accept that each discount is applied to the current price, not the original one. But it does mean the headline framing ("30% + 10%!") reads more generous than the math actually delivers, and that gap tends to widen the more discounts get stacked. Three or four layered promotions compound the same way, and the real total savings ends up noticeably below what simple addition would suggest every time.
The general rule
To find the true combined discount, convert each percentage to what you're actually paying, then multiply those together. 30% off means paying 70% of the price; 10% off means paying 90% of whatever's left. Multiply 0.70 × 0.90 and you get 0.63 — meaning you pay 63% of the original price, or a genuine 37% off, not 40%. The more discounts get layered on, the more this compounding effect pulls the real number below the "just add them up" instinct.
Reckon's Discount Calculator handles the stacking automatically — enter the original price and both discount percentages, and it shows the real final price and the true combined percentage off, no mental math required.
Open the Discount Calculator →The takeaway
Stacked discounts are still real savings — just not quite as much as the headline number implies. Knowing the actual math means you can compare a "30% + 10%" sale against a flat "35% off" sale accurately, instead of assuming the stacked one automatically wins because the numbers look bigger added together.