Online Tool Store
Discount Calculator
Work out what you actually pay after a discount, including stacked offers and tax, with the saving and effective percentage shown. Runs in your browser.
🔒 This tool runs entirely in your browser. Your files are never uploaded to a server.
You pay
—
Example shown — enter your own numbers. Any currency; only the figures matter.
- Original price
- After first discount
- After extra discount
- Tax added
- Total saved
- Effective discount
How it works
- Enter the original price and the discount — either a percentage or a flat amount off.
- Add a second percentage discount if the offer stacks, and a tax rate if one applies.
- The total updates as you type, with each step shown in the breakdown underneath.
- Check the effective discount to see what the offer is really worth.
The formula, and why stacked discounts mislead
Each percentage discount multiplies what is left, rather than subtracting from the original:
total = price × (1 − d₁) × (1 − d₂) × (1 + tax)
effective discount = 1 − (1 − d₁) × (1 − d₂)
Take 120 with 25% off: 120 × 0.75 = 90. Add a further 10% and it is 90 × 0.90 = 81, so you have saved 39 of the original 120 — an effective 32.5% off, not the 35% that adding the two percentages suggests. The two discounts never sum, because the second one is taken from a smaller number.
The same reasoning explains why deep stacked offers never reach zero: 50% off twice is 0.5 × 0.5 = 0.25, so you still pay a quarter of the original price. And it is why a flat amount behaves differently from a percentage — a fixed 20 off is worth much more on a 40 item than on a 400 one.
FAQ
Why is 20% off then 10% off not 30% off?
Because the second discount applies to the already-reduced price, not the original. On 100, 20% off leaves 80, and 10% of 80 is 8, so you pay 72 — an effective 28% off, not 30%. The gap widens as the discounts get bigger, which is why the effective figure is shown separately.
Does the order of two discounts matter?
Not for the final price — multiplying by 0.8 then 0.9 gives the same result as 0.9 then 0.8. It matters only when one of them is a fixed amount rather than a percentage, in which case taking the fixed amount off first leaves you paying less.
Is tax applied before or after the discount?
After, which is how retail pricing normally works: the discount reduces the taxable amount, then tax is charged on what remains. That is why the tax row appears at the end of the breakdown.
Why does "you save" ignore the tax?
So it compares like with like. The original price shown is before tax, so the saving is measured before tax too — otherwise adding a tax rate would appear to shrink your discount, which would be misleading.
Which currency does it use?
None in particular — it works with plain numbers, so it is correct for any currency. Figures are shown to two decimal places using your device's regional number formatting.
What happens if the discount is bigger than the price?
The total stops at zero rather than going negative, and a note explains why. A percentage above 100% is capped at 100% for the same reason — no shop pays you to take an item away.
How we compare
| Feature | Online Tool Store | Ad-supported calculator sites | Phone calculator |
|---|---|---|---|
| Handles stacked discounts correctly | ✓ | Many only take one discount | Only if you do the maths yourself |
| Shows the effective percentage | ✓ | Rarely | ✗ |
| Step-by-step breakdown | ✓ | Sometimes | ✗ |
| No ads, nothing typed is sent anywhere | ✓ | ✗ | ✓ |
| Works with no connection at all | Offline once loaded | ✗ | ✓ |
| Compares several items at once | ✗ | A few offer a basket view | ✗ |
Most useful standing in a shop working out whether "extra 10% off sale items" is the bargain it sounds like — the effective percentage answers that in one glance. It handles one item at a time; for a whole basket, a spreadsheet is still faster.