Discount Calculator
Work out what a sale price really comes to, including a second stacked discount and sales tax — or go the other way and find the discount percentage hidden behind two prices.
Applied to the already-reduced price.
Added after the discounts, on the reduced price.
How to use this calculator
The calculator has two tabs, depending on which number you are missing.
Find sale price
- Enter the original price and the advertised discount percentage.
- Add a second discount if the shop is stacking offers — it is applied to the reduced price, which is how nearly every retailer does it.
- Add your sales tax rate if you want the true till price. Tax is calculated on the discounted amount.
- Read off the final price, the amount saved and the effective discount across both offers.
Find discount %
- Enter the original price and the price on the tag.
- The calculator shows the discount percentage, the amount saved, and what fraction of the original price you are still paying.
- If the second price is higher than the first, it is flagged as a price increase rather than a discount.
The formula
A single discount is two lines of arithmetic:
saving = original price × (discount ÷ 100)
sale price = original price − saving
A second discount multiplies down from the new price rather than the old one:
final price = original × (1 − d1 ÷ 100) × (1 − d2 ÷ 100)
effective discount % = (original − final) ÷ original × 100
Sales tax is then charged on what is left:
price with tax = discounted price × (1 + tax ÷ 100)
And to work backwards from two prices:
discount % = (original − sale) ÷ original × 100
Worked examples
A straightforward 30% off
A jacket marked $80 at 30% off.
- Saving: 80 × 0.30 = $24.00
- Sale price: 80 − 24 = $56.00
Stacked discounts: 40% off, then an extra 20%
Boots at $120 with 40% off, plus a clearance coupon for another 20%.
- After the first discount: 120 × 0.60 = $72.00
- After the coupon: 72 × 0.80 = $57.60
- Total saved: 120 − 57.60 = $62.40
- Effective discount: 62.40 ÷ 120 = 52%, not 60%
With sales tax added
A $59.99 item at 30% off, in a state with 8.25% sales tax.
- Discount: 59.99 × 0.30 = $18.00, leaving $41.99
- Tax: 41.99 × 0.0825 = $3.46
- Total at the till: $45.45
Frequently asked questions
No. The second discount comes off the already-reduced price, not the original. On a $120 item, 40% off leaves $72, and 20% off that leaves $57.60 — a total saving of 52%, not 60%.
Stacked discounts always come out lower than the sum of the two percentages. The calculator shows the effective discount so you can see the real figure.
After. Tax is charged on what you actually pay, so the discount is applied first and the tax rate is then applied to the reduced price. That is the order this calculator uses.
It also means a discount saves you a little tax as well as the sticker reduction.
Find 10% by moving the decimal point one place left, then build from there. 30% off a $80 item is three lots of $8, so $24 off and $56 to pay.
For 25% off, halve the price and halve it again to get the saving. For 15%, take 10% and add half of it.
Divide the sale price by 1 minus the discount as a decimal. An item on sale at $57 after 25% off started at 57 ÷ 0.75 = $76.
If you know both prices but not the percentage, use the Find discount % tab instead.
For two identical items, yes. You pay 1.5 items instead of 2, which is 75% of the full price — a 25% discount overall.
If the offer applies the discount to the cheaper item and the items have different prices, the effective saving is smaller than 25%.
A discount going from 20% to 25% is a rise of 5 percentage points, but a 25% increase in the discount itself. The two are easy to mix up in advertising.
This calculator always works in plain percent of the original price, which is the figure that matters at the till.