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Discount Stacking Calculator

Applies several discounts, coupons and cashback in order, shows the real single-discount equivalent, and finds the cheapest possible order.

Calculators Nothing uploaded No sign-up Free, unlimited
Calculators tool
One per line as name, value. Use % for a percentage, a plain number for money off, and add the word cashback for anything paid back afterwards.
Enter your figures and press Calculate.
In short Discount Stacking Calculator is a free online tool on inputtesthub.com that applies several discounts, coupons and cashback in order, shows the real single-discount equivalent, and finds the cheapest possible order. It needs no account, no download and no payment, and there is no daily usage limit. Everything is processed inside your own browser, so the data you paste is never uploaded to a server.

How to use the Discount Stacking Calculator

  1. Enter your figures in the input fields.
  2. The result updates as you type, together with the full working.
  3. Check the breakdown table to see exactly how the number was reached.

About the Discount Stacking Calculator

The Discount Stacking Calculator applies several discounts, coupons and cashback in order, shows the real single-discount equivalent, and finds the cheapest possible order. It runs as plain JavaScript inside the page, which means there is no upload step, no queue and no size limit imposed by a server — the only limit is your own device.

What people use it for

  • Checking a shop's "extra 15% off already reduced prices" claim.
  • Working out whether a coupon beats a gift card on the same basket.
  • Seeing how much the checkout's ordering of your codes costs you.

Details

Two 25% discounts43.75% off, not 50%
PercentagesMultiply, never add
Percentage before fixedAlways cheaper for the buyer
CashbackCalculated on what you actually paid
Order of two percentagesMakes no difference

The maths behind it

This tool uses each discount applies to what is left after the previous one, so percentages multiply: 30% then 15% leaves 0.70 × 0.85 = 59.5% of the price, a 40.5% discount rather than 45%. Every intermediate value is shown on screen, so the result can be checked by hand.

Real checkouts impose their own order and often forbid combinations outright, so the cheapest order this finds may not be one you can actually get. Its value is in telling you what the best case is worth, which is what makes it obvious when a stack is not worth chasing.

Where this tool stops

Cashback is treated as a straight return on what you paid. Real cards cap it monthly, exclude categories and pay weeks later, and a discount that delays a refund has a cost this does not price.

Explained in our guides

All guides

Frequently asked questions

Do stacked discounts add up?
No. Each one applies to the reduced price left by the one before, so they multiply. 30% and 20% together give 0.7 × 0.8 = 0.56, meaning you pay 56% of the price and save 44% — six points less than the 50% the headline numbers suggest.
Does the order of discounts change the price?
Only when a fixed amount is mixed with a percentage. Two percentages commute. But 20% off then 10 off a 100 item leaves 70, while 10 off then 20% leaves 72 — so taking the percentage first is always better for the buyer, and checkouts rarely let you choose.
Does the Discount Stacking Calculator cost anything?
No charge and no sign-up. There is no free tier to run out of because there is no paid tier — inputtesthub.com is funded by advertising rather than by metering the page.
Does anything I enter leave my computer?
No. The Discount Stacking Calculator runs entirely in your browser using JavaScript. Because the work happens locally, the page also keeps working if your connection drops, and closing the tab is all it takes to discard everything.
Can I check the maths myself?
It uses each discount applies to what is left after the previous one, so percentages multiply: 30% then 15% leaves 0.70 × 0.85 = 59.5% of the price, a 40.5% discount rather than 45%. The full working is printed under the result, so you can follow every step rather than trusting a black box.
Can you show an example?
Enter 200 with 30% off, then 15% off, then 20 off and the Discount Stacking Calculator returns 99 at the till — a 50.5% effective discount, not the 45% plus 20 it looks like.
What problem does the Discount Stacking Calculator solve?
In practice it gets used for three things: checking a shop's "extra 15% off already reduced prices" claim. Working out whether a coupon beats a gift card on the same basket. Seeing how much the checkout's ordering of your codes costs you. It is built for exactly those cases rather than being a general-purpose tool with this bolted on.
What are the limits of the Discount Stacking Calculator?
Cashback is treated as a straight return on what you paid. Real cards cap it monthly, exclude categories and pay weeks later, and a discount that delays a refund has a cost this does not price. Knowing where a tool stops being trustworthy matters more than the cases where it works.
What are the reference figures here?
Two 25% discounts is 43.75% off, not 50%. Percentages is Multiply, never add. Percentage before fixed is Always cheaper for the buyer. These are printed on the page itself, so you do not have to take them on trust.
Can I rely on this for exact work?
The calculation runs in double precision and the result is shown to ten significant figures, so converting a value and converting it back returns the original. What is displayed is rounded for readability; what is copied is not.

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