Discount Calculator

Sales signs and discount codes are not always as straightforward as they look, particularly when discounts are combined, or when you are trying to compare a percentage-off deal against a fixed amount-off voucher. This calculator works out the final price, the amount you save, and the effective discount rate, for either type of offer.

How to use the discount calculator

Enter the original price, then choose whether your discount is a percentage off or a fixed amount off. For a percentage discount, enter the percentage, such as 20 for 20% off. For a fixed amount, enter the pounds and pence taken off, such as £15 off. The calculator instantly shows the final price, how much you save, and the equivalent effective discount percentage either way, so you can compare offers on a like-for-like basis.

How the calculation works

For a percentage discount, the amount saved is simply the original price multiplied by the discount percentage. The final price is the original price minus that saving. For a fixed amount off, the calculation works the other way: the saving is whatever fixed amount you enter, and the effective discount percentage is that saving divided by the original price, expressed as a percentage.

This effective percentage figure is particularly useful for comparing two different types of offer. A £15 off voucher and a 15% off voucher only save the same amount at one specific price point, £100, and diverge from each other at every other price, sometimes significantly.

Worked example

Say a jacket is priced at £80, reduced by 20%. The saving is £80 × 0.20 = £16, giving a final price of £64.

Now compare that to a different shop offering the same jacket at £80 with a £20 off voucher instead. That voucher saves more in cash terms, £20 rather than £16, and works out at an effective discount of 25%, a better deal than the 20% offer despite looking similar at first glance. Try switching between percentage and amount modes in the calculator above with your own prices to compare real offers you have seen.

Comparing discount codes and voucher offers

Online shopping often presents several different types of offer at once: a site-wide percentage discount, a fixed-amount voucher code, and sometimes free delivery thrown in on top. Working out which combination actually saves the most money is not always obvious from the checkout page alone, particularly when a voucher only applies above a minimum spend or excludes certain items.

A useful habit is to work out the effective percentage saved for each offer using this calculator, then compare that percentage directly rather than comparing a percentage offer against a pounds and pence offer at face value. This is especially useful when a retailer offers a choice between two vouchers, such as £10 off everything or 15% off orders over £50, since the better choice depends entirely on how much you are actually spending.

It is also worth checking whether a discount is being calculated on the price before or after any other reductions, such as an existing sale price. Retailers sometimes apply a voucher to the already discounted sale price, and sometimes only to full-price items, so reading the terms attached to a code before assuming it will apply to everything in your basket can save disappointment at checkout.

Common mistakes to avoid

The most common mistake is assuming stacked discounts simply add together. Two 20% discounts applied one after another do not equal 40% off. The first discount takes £80 down to £64. The second 20% discount then applies to £64, not the original £80, taking a further £12.80 off, for a final price of £51.20, an effective discount of 36%, not 40%. Always apply stacked discounts one at a time, in sequence, rather than adding the percentages upfront.

Another mistake is comparing a percentage-off deal and an amount-off deal purely on the headline number without checking the actual price. A “25% off” sign sounds more impressive than “£10 off”, but on a £30 item, 25% off only saves £7.50, less than the flat £10 voucher would. Running both through this calculator removes the guesswork.

It is also worth checking whether a discount applies before or after VAT, and whether delivery or other charges are added afterwards, since these can quietly erase some or all of an advertised saving once the full transaction is complete.

Why the effective discount rate matters

The effective discount rate this calculator shows is more useful than it might first appear, because it puts every type of offer on the same scale. A fixed amount off, a percentage off, and even a buy-one-get-one-half-price deal (once averaged across both items) can all be converted into a single comparable percentage, making it much easier to judge which deal is genuinely the better one rather than relying on which offer is phrased more persuasively.

This is particularly useful when budgeting for a larger purchase, where even a few percentage points of difference between two offers can add up to a meaningful amount of money. Working the numbers through properly, rather than trusting the headline claim on a sign or banner, is a small habit that consistently pays off over time.

Related calculators

For everyday maths beyond discounts, our percentage calculator covers percentage change, increase and decrease in general, and our tip calculator works out a tip and splits a bill between diners. If you need to add or remove VAT from a price, our VAT calculator handles that separately. Whatever you save on a good discount is also worth putting to work: our guide to compound interest explains how even small regular savings can add up significantly over time.