How to Calculate a Discount (and Why Two Discounts Don't Add Up)

To calculate a discount, open the Discount Calculator, enter the Original price and Discount %, and read the Final price instantly — add an Extra discount % (stacked) or Sales tax % if either applies, and every intermediate number is shown too.

What the Discount Calculator does

A single percent-off sale is simple multiplication, but two things trip people up: stacking a second discount on top of the first (it's not as simple as adding the percentages), and whether sales tax applies before or after the discount. The Discount Calculator takes an original price, one or two discount percentages, and an optional tax rate, then shows the final price along with how much you saved, the combined ("effective") discount rate, the price after just the first discount, and the tax amount.

How to calculate a discount with Toolbench

1. Open the Discount Calculator.
2. Enter the Original price.
3. Enter the Discount % for the main sale.
4. If a second discount stacks on top (a coupon code on top of a clearance price, say), enter it in Extra discount % (stacked) — leave it at 0 if there's only one discount.
5. If tax applies, enter the Sales tax %. It's calculated on the discounted price, not the original.
6. Read Final price in the large result box — click it to copy the number.
7. Below it, You save, Effective discount, Price after first discount, and Tax each show their own value — click any row to copy it.
8. Click Copy results to copy everything as plain text.

Example: a single discount

The tool opens with Original price 80 and Discount % 25:

Original price	80
Discount %	25
Final price	60.00
You save	20.00
Effective discount	25%
Price after first discount	60.00
Tax	0.00

25% off 80 is 60.00 — straightforward, since there's only one discount and no tax.

Example: stacking two discounts plus tax

Now try a $200 item with 30% off, an extra 10% off stacked on top, and 8% sales tax:

Original price	200
Discount %	30
Extra discount % (stacked)	10
Sales tax %	8
Price after first discount	140.00
Effective discount	37%
You save	74.00
Tax	10.08
Final price	136.08

The first discount brings 200 down to 140.00. The second discount (10%) applies to that 140.00, not the original 200 — so it knocks off 14.00, landing at 126.00 before tax. That's a 37% effective discount, not 40%. Tax is then calculated on the discounted 126.00 (8% = 10.08), giving a final price of 136.08.

Reference: why stacked discounts aren't additive

Two discounts stacked together are always a little less generous than their sum, because the second one is a percentage of an already-smaller number:

Discount 1	Discount 2	Looks like	Effective discount
20%	10%	30%	28%
25%	25%	50%	43.75%
30%	10%	40%	37%
50%	50%	100%	75%

Notice stacking two 50% discounts never gets you to free — it gets you to 75% off, since the second half-price cut only applies to the half that's left.

Tips and common mistakes

• Stacked discounts multiply, they don't add. "30% off, plus an extra 10% off" is 37% off total, not 40% — each discount applies to the price left after the one before it.
• Check whether tax applies before or after the discount. The Discount Calculator applies tax to the discounted price (the common approach at checkout), so the tax line reflects what you'd actually be charged, not tax on the sticker price.
• "Effective discount" is the number that matters for comparing deals, not the sum of the two percentages — use it to compare a "30% + 10%" promotion against a flat "35% off" one.
• Leave Extra discount % at 0 if you're only working with a single discount; it won't change the result.

Related tools

• Percentage Calculator — percent of, percent change, increase and decrease, for percentage math beyond discounts.
• Sales Tax Calculator — add tax to a price or back it out of a tax-included total.
• Margin Calculator — work out profit margin and markup from cost and price.
• Loan Calculator — monthly payment, total interest and payoff date for a loan.

Frequently asked questions

Do two stacked discounts add up to their sum?

No. A 30% discount followed by a 10% discount is 37% off total, not 40%, because the second discount is calculated on the already-discounted price rather than the original.

Does sales tax apply before or after the discount?

In the Discount Calculator, tax is calculated on the price after both discounts, which matches how most retail checkouts apply tax — you're taxed on what you actually pay, not the original sticker price.

What does effective discount mean?

It's the single percentage that the combination of your original price and final price works out to — useful for comparing a stacked discount against a flat one without doing the multiplication yourself.

Is my data sent to a server when I use the Discount Calculator?

No. The calculation happens in your browser as you type. If you're signed in, your inputs sync privately to your account; if you're signed out, nothing is saved anywhere.

Can I use this for just one discount?

Yes — enter the Original price and Discount %, and leave Extra discount % (stacked) at 0 and Sales tax % at 0 if neither applies.