Discount and Sales Tax Calculator
Find the real price after one discount or two, with tax added and the unit price worked out.
The first or only percentage off.
For stacked offers. Applied to the already-reduced price.
Added after the discount.
For a unit price.
Enter an amount to see which offer wins.
You pay
$56.00
- You save
- $24.00
- Total off
- 30%
- After discount
- $56.00
- Tax
- $0.00
Everything here runs on your device. Nothing you enter is uploaded or stored.
Enter a price and a discount and this gives you the sale price, the amount saved, and the total once tax is added. It also handles the two situations that trip people up in a shop: offers that stack, and offers that are quoted in different shapes so they cannot be compared at a glance.
How to use it
- Enter the original price as printed on the label or the shelf edge.
- Enter the discount percentage, or press one of the presets for 10, 20, 25, 30 or 50 per cent.
- If the shop is stacking a second offer on top, enter that percentage too.
- Add your local sales tax or VAT rate if you want the till price rather than the shelf price.
- For a multi-pack, enter how many items are in it to get a comparable unit price.
- To compare against a flat-amount offer, enter that amount and the calculator will say which is better.
Why stacked discounts are smaller than they look
This is the part worth understanding, because it is the most common arithmetic mistake in retail.
If a shop offers 30% off and then takes a further 20% off at the till, the instinct is to add them and expect 50% off. That is not what happens. The second discount applies to the price left by the first one, not to the original.
Work it through on a $100 item. Thirty per cent off leaves $70. Twenty per cent off that $70 is $14, leaving $56. You paid $56, so the total discount was 44%, not 50%. The gap widens as the percentages grow: 50% then 50% is 75% off, not 100% off, which is why nothing is ever free after two half-price offers.
The general rule is that you multiply what remains rather than adding what is taken. Thirty per cent off leaves 70% of the price, and 20% off leaves 80% of that, so you pay 0.70 × 0.80 = 0.56, or 56% of the original. This calculator shows the single equivalent percentage whenever a second discount is in play, and it explicitly points out when that figure differs from the naive sum — which it always does.
Order does not matter, incidentally. Thirty then twenty gives the same result as twenty then thirty, because multiplication is commutative. What does matter is whether a flat amount is involved: $20 off then 20% off is not the same as 20% off then $20 off, and the difference can be several pounds.
What it does not do
It does not know your local tax rate, and rates vary by state, county and sometimes by product category, so you have to enter it. It does not handle buy-one-get-one or three-for-two offers directly, though you can approximate those with the unit price field: three items for the price of two is a 33.3% discount on the pack. It also has no opinion on whether something is good value — it only tells you what you will pay.
Everything runs in your browser. No prices, and nothing else you type, is sent anywhere.
What each discount actually leaves you paying
| Discount | You pay | On $100 | On $250 |
|---|---|---|---|
| 10% off | 90% | $90.00 | $225.00 |
| 20% off | 80% | $80.00 | $200.00 |
| 25% off | 75% | $75.00 | $187.50 |
| 33% off | 67% | $67.00 | $167.50 |
| 50% off | 50% | $50.00 | $125.00 |
| 70% off | 30% | $30.00 | $75.00 |
Common stacked combinations
| First | Then | Naive sum | Actual discount | Pay on $100 |
|---|---|---|---|---|
| 10% | 10% | 20% | 19% | $81.00 |
| 20% | 10% | 30% | 28% | $72.00 |
| 30% | 20% | 50% | 44% | $56.00 |
| 40% | 25% | 65% | 55% | $45.00 |
| 50% | 20% | 70% | 60% | $40.00 |
| 50% | 50% | 100% | 75% | $25.00 |
Questions
Does 30% off then 20% off equal 50% off?
No. The second discount applies to the already-reduced price, so 30% then 20% is 44% off in total. On a $100 item you pay $56, not $50. Stacked percentages always come out smaller than their sum.
Is tax calculated before or after the discount?
After. Sales tax and VAT apply to the price you actually pay, so a discount reduces the tax as well. This calculator applies every discount first, then adds tax to the reduced figure.
Which is better, 20% off or $20 off?
It depends entirely on the price. They are equal at $100. Below that the flat $20 wins, above it the percentage wins. Enter both and the calculator names the better one and the margin.
What does the unit price tell me?
It divides the final price by the number of items, which is the only reliable way to compare a six-pack against a twelve-pack. Shelf labels often show unit prices in different units for the same product.
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