How do stacked discounts combine?

Multiply keep-factors: (1−d₁)×(1−d₂). 35% then 10% = 0.65×0.90 = 0.585 → 41.5% off combined, not 45%.

How do I find the original price from a sale price?

Divide by the keep-factor: original = sale ÷ (1 − d/100). A £78 item at 35% off was 78 ÷ 0.65 = £120.

Is discount applied before tax?

Almost always yes — tax applies to what you actually pay. US: ($100−20%) + 8% tax = $80×1.08 = $86.40.

What is a good discount?

Context beats rules: 10–15% is strong for Apple-style fixed pricing; 40%+ is routine for fast fashion at season end. Compare unit prices, not just %.

How do I calculate percent off from two prices?

(Was − Now) ÷ Was × 100. £120→£78 = 42÷120 = 35% off. Use our Percentage Change calculator for signed reporting.

Financial · Free tool

Discount Calculator

Sale price, savings and stacked discounts — with optional tax.

A £120 coat at 35% off — do you pay £78? What if an extra 10% code applies, and then 20% VAT? Most shoppers (and many tills) get the second step wrong by adding percentages instead of compounding them. This discount calculator returns the discount amount, price after discount, and after-tax total in one pass, with an honest effective-discount figure so 'up to 70% off' claims meet reality.

Retail maths is sequential multiplication, not addition. 35% off means pay 65% (×0.65); a further 10% off means ×0.90 on the already-reduced price — a combined factor of 0.585, i.e. 41.5% off, not 45%. Tax then multiplies again (×1.20 for 20% VAT in the UK). The tool chains these correctly and shows each line, which is also how trading-standards officers expect reductions to be evidenced: original, intermediate, and final prices all visible.

Enter original price, discount percent, and optional tax. Compare two sale rails side-by-side with Reset between runs — e.g. '30% off £85' vs '£60 + 10% code' — and let the after-tax totals decide.

Updated 2026-09-01 · 6-min read · Formula + steps included

● Discount workstation

Financial →

Discount formulas

discount = price × d/100 • sale = price − discount • stacked: price × (1−d₁) × (1−d₂) • with tax: sale × (1+t/100)

Each percentage becomes a keep-factor (1 − d). Single discounts subtract once; stacked coupons multiply keep-factors; sales tax multiplies the discounted price by (1 + t). Effective discount = discount ÷ original × 100.

price: Original (was) price before any reduction.
d: Discount percent 0–100. Stacked codes apply sequentially, not additively.
t: Sales tax / VAT percent applied after discount (UK 20% standard).

Worked example: £120, 35% off + 10% code + 20% VAT

Black-Friday style stacking done right:

First cut: £120 × 35% = £42 off → pay £78 (factor 0.65).
Code: £78 × 10% = £7.80 off → pay £70.20 (×0.90; combined 0.65×0.90 = 0.585).
VAT: £70.20 × 1.20 = £84.24 final.
Effective discount: (£120 − £70.20) ÷ £120 = 41.5% pre-tax — not 45%.
Naive adding (35+10=45%) would claim £66 pre-tax — £4.20 too low. Tills use the correct £70.20.

Result: Pre-tax £70.20 (save £49.80, 41.5% off). With 20% VAT: £84.24.

How to use this discount calculator

Built for aisle-speed comparisons.

Step 1: Enter original price

The 'was' price. For price-match claims, use the competitor's shelf price, not RRP.

Step 2: Enter discount %

Single code or headline reduction. For two codes, run once, then run the result through again with the second %.

Step 3: Add tax if needed

UK shoppers: prices usually include VAT, so leave tax 0. US shoppers: add state sales tax for the out-the-door total.

Step 4: Compare and decide

Note the sale and savings lines, Reset, and run the rival deal. Lowest after-tax total wins.

Use cases

Beyond the high street:

Sale rails

'40% off £65' = £39. 'Buy one get one half price' on two £50 items = £75, i.e. 25% off the pair — the tool proves which rail is cheaper.

Coupon stacking

15% newsletter + 10% student codes = 1 − 0.85×0.90 = 23.5% off, not 25%. Retailers cap stacking; test both orders (result is identical).

Trade & bulk

Contractors comparing '£2,400 less 12.5%' (£2,100) vs '£2,050 net' see the £50 gap instantly, before VAT.

Hospitality

Early-bird 20% off a £90 tasting menu = £72; service 12.5% on the reduced bill = £81 total, not £90+.

Resellers

Margin check: buy at 60% off RRP (£40 on £100), sell at 20% off (£80) → £40 gross margin before fees.

Pro tips

Shop like a pricing analyst:

Convert % to keep-factor instantly: 30% off → pay 0.70×. Multiply in your head for sub-£100 items.
Beware 'up to X% off' — the headline applies to one size/colour. Scan the actual ticketed reduction.
Annualise subscriptions: '20% off monthly £12' (£115/yr) vs '£99 annual' — the flat £99 wins by £16.
Screenshot was/now + date for Consumer Protection claims; 'was' must be genuine (28+ days at higher price).
Factor cashback separately: 5% top-cashback on the discounted price stacks multiplicatively too.