Percent off is easy; stacked discounts are not
A single discount is one multiplication: 20% off ₹100 leaves ₹80. The arithmetic only gets interesting when a second discount is applied on top, and that is precisely where shops advertise hardest and shoppers most often overestimate the saving.
20% off plus an extra 10% off is not 30% off. The second discount is taken from the already-reduced price, not from the original. ₹100 becomes ₹80, and 10% off ₹80 is ₹72 — an effective discount of 28%, not 30%. The gap is small on a ₹100 item and considerably less small on a ₹50,000 one, and it always favours the shop.
Using this discount calculator
Enter the original price and the discount. The results show the final price and what you save. Two optional settings live in the customize panel, and both are off by default:
Extra discount turns on a second percentage, applied after the first — the stacked-coupon case above. Switching it on also reveals an effective discount row, which is the number worth quoting: it tells you what single discount would have produced the same final price, so you can compare a stacked offer against a flat one honestly.
Sales tax adds tax to the discounted price and shows the amount added, so the final figure is what you will actually be charged rather than the shelf price.
The formula, worked through
A discount is a multiplication by (1 − rate). Chain them and you multiply again.
₹100 at 20% off is 100 × 0.80 = ₹80, a saving of ₹20. Add a stacked 10%: 80 × 0.90 = ₹72, total saving ₹28, effective discount 28%. Now switch sales tax on at 8% and the tax is charged on ₹72, not on the original — 8% of 72 is ₹5.76, for a final ₹77.76.
The order of operations there is the point. Discount first, tax second, is how essentially every jurisdiction handles it: you are taxed on what you pay, not on what the item was once listed at. It is also why a coupon saves you slightly more than its face value once tax is in the picture — it removes the tax on the discounted portion too.
Reading an offer properly
A few patterns worth recognising. “Buy one get one 50% off” is a 25% discount across the two items, not 50%. “Up to 70% off” describes the single best line in the store and nothing about the item you want. And a percentage off an inflated “was” price is a discount on a number, not on a value — the only meaningful comparison is the final price against what the same item costs elsewhere, which is why the final price is the primary result on this page rather than the saving.
One more, for stacked offers specifically: the order the discounts are applied in does not change the outcome. 20% then 10% and 10% then 20% both land on ₹72, because multiplication does not care about order. If a shop insists otherwise, something other than arithmetic is going on.
For the underlying percentage maths — what percent one number is of another, or the change between two — see the percentage calculator.
FAQ
How do I work out the original price from a sale price?
Divide, do not add the percentage back. If an item is ₹72 after 28% off, the sale price is 72% of the original, so the original is 72 ÷ 0.72 = ₹100.
Adding 28% to ₹72 would give ₹92.16, which is wrong for the same reason removing a tax by subtraction is wrong: the percentage was taken from the larger number, so it has to be divided back out of the smaller one.
Which is better, 30% off or ₹30 off?
It depends entirely on the price. They are identical at ₹100 — 30% of 100 is 30. Below ₹100 the flat amount wins; above it the percentage does, and the gap widens fast.
On a ₹40 item, ₹30 off is a 75% discount and the percentage offer saves you ₹12. On a ₹500 item the percentage saves ₹150 against the flat offer's ₹30. If you are given the choice, the break-even is simply the flat amount divided by the percentage.
How do you calculate a discount?
Multiply the original price by the discount percentage (as a decimal) to get the discount amount, then subtract that from the original price:
Why isn't 20% off plus 10% off the same as 30% off?
Stacked discounts apply one after another, not on top of each other — the second discount is taken from the already-reduced price:
The gap grows with bigger percentages, which is why "stack these coupons" promotions are worth less than the two numbers suggest. Turn on "Extra discount" in the customize panel to see the effective rate for your own numbers — it only appears in the results once that toggle is on.
Is sales tax charged before or after a discount?
In most U.S. states, sales tax applies to the price you actually pay — after a store discount or coupon is subtracted, not the original sticker price:
Manufacturer coupons and rebates are sometimes taxed differently from store-issued discounts, and a handful of states have their own rules, so check local guidance for anything beyond an estimate. This calculator follows the common order above — tax is only added to your results when "Sales tax" is switched on.
What's the difference between percent off and dollar off?
A percent-off discount scales with price — a flat dollar-off discount doesn't:
| Item price | 20% off | $10 off |
|---|---|---|
| $20 | $4.00 (20%) | $10.00 (50%) |
| $50 | $10.00 (20%) | $10.00 (20%) |
| $200 | $40.00 (20%) | $10.00 (5%) |
A flat-dollar coupon is proportionally more valuable on cheaper items. To compare a dollar-off coupon against a percent-off one, divide the dollar amount by the price and multiply by 100 to get its effective percentage.