About the Discount Calculator
This discount calculator gives you the number that actually matters at the till: what you pay after the reduction, and what the saving really is. Beyond a single percent off, it handles a second discount stacked on top — the extra-20%-off-sale-prices offer — and works out the true effective discount, which is always less than the two figures added together. An optional tax field then applies sales tax, VAT or GST to the reduced amount, which is how nearly every tax system treats a genuine discount.
How to use the Discount Calculator
- 1
Enter the Original price as shown on the ticket before any reduction.
- 2
Enter the Discount percentage advertised.
- 3
If a second offer applies to the already-reduced price, enter it as Extra discount on top.
- 4
Add a Tax added after discount percentage if the displayed price excludes tax.
- 5
Read what you pay, what you save and the effective discount across both reductions.
What people use it for
Decoding stacked sale offers
A 40% off rail with a further 20% off at the till sounds like 60% off. Entering both shows an effective 52% discount, which is a meaningful difference on a 200 item.
Comparing coupon codes
Test a percentage code against the same item at a different retailer's base price. The you-pay figure settles it instantly regardless of how the offer is framed.
Retail and market stall pricing
Sellers can work out a markdown that hits a target ticket price, and see what the effective discount looks like to a customer before printing the signage.
Why stacked discounts never add up
Each discount applies to whatever the price is at the moment it is taken, not to the original. Multiply rather than add: a discount of d1 followed by d2 leaves you paying (1 − d1/100) × (1 − d2/100) of the original. Twenty percent then a further ten percent gives 0.80 × 0.90 = 0.72, so you pay 72% and the effective discount is 28%, not 30%. Forty then twenty gives 0.60 × 0.80 = 0.48, an effective 52% rather than 60%. The gap widens as the discounts grow: 50% then 50% leaves you paying 25%, not zero. A useful shortcut is that the shortfall equals the product of the two discounts divided by 100 — for 20 and 10 that is 200 ÷ 100 = 2 percentage points, exactly the difference between 30 and 28. The order of the discounts makes no difference to the final price, since multiplication commutes, though it can matter for how a retailer's system applies coupon eligibility rules.
Where tax sits in the sequence
This calculator applies tax after both discounts, which reflects standard practice in VAT, GST and most US sales tax regimes: tax is charged on the consideration actually paid, so a genuine price reduction reduces the tax as well. On a 1,200 item with 25% off and 18% tax, the discounted price is 900, the tax is 162 and you pay 1,062 — the tax bill falls to 162 from the 216 the undiscounted price would have attracted. The distinction matters in two edge cases. Manufacturer rebates and third-party coupons, where the retailer is reimbursed, are often taxed on the pre-coupon price because the shop still receives full value. And in markets where displayed prices are already tax-inclusive, such as most of Europe, the discount is applied to the gross figure and you should leave the tax field at zero to avoid double-counting. If you need to split a tax-inclusive figure into net and tax components, the GST calculator does that directly.
Tips
- Judge a sale by the amount you pay, not the percentage saved — a 70% reduction on an overpriced item can still be poor value.
- Check whether a second discount applies to the sale price or the original; a few retailers stack against the original, which is genuinely better.
- For buy-one-get-one-free, enter 50% as the discount and treat the total as covering two units.