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Deals & Discounts Calculator

Work out exactly what you save with any deal — and see the full step-by-step working so you understand why, not just what.

DEALS & DISCOUNTS CALCULATOR

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Step-by-step solution

Select a deal type and enter a price to see the working

Deals & Discounts Calculator Explained

Core concepts, classroom applications, and plain-English explanations for all audiences.

When would you actually use this?

Every time you're standing in a supermarket aisle comparing "3 for £5" vs "£1.49 each". Or at a clothes sale where "buy 2 get 1 free" sounds great but you only wanted one item. Deal maths is the difference between a genuine saving and just spending more.

Worked example

"Which is better: 3-for-2 on £24.99 shirts, or 40% off any shirt?"

3-for-2: Pay for 2, get 3 → £49.98 for 3 shirts

Cost per shirt: £49.98 ÷ 3 = £16.66

40% off one: £24.99 × 0.60 = £14.99

Result: 40% off wins — but only if you need 1, not 3

The 3-for-2 costs £49.98 total. If you only want 1 shirt, the "deal" is no saving at all.

Deal types decoded

  • → BOGOF: Buy one get one free = 50% off each, but only if you need two
  • → Cheapest item free: Add three items of different prices — you save the cost of the cheapest one only
  • → Multi-buy (e.g. 3 for £5): Calculate cost per unit — 3 for £5 is £1.67 each; compare to the single-item price

The quantity trap

A deal is only a saving if you were going to buy that quantity anyway. Buying 3 shampoo bottles to "save" on a deal you didn't need means you've spent more, not less — even if the unit price is lower.

Good to know

Understanding deals

BOGOF is 50% off — but only if you need 2
Buy One Get One Free sounds like a great deal. And it is — but only if you actually need two of the item. If you only needed one, you're spending double to "save" money.
Need 1: you spend £1.80 — no saving
Need 2: you spend £1.80 — save £1.80 (50%)
Need 3: buy 2 packs (BOGOF x2) — save 50%
Common mistake
"Cheapest free" is often less than you think
When you buy 3 items and get the cheapest free, the saving depends entirely on how different the prices are. If all 3 items cost the same, it's 33.3% off. If the cheapest is much cheaper than the rest, the saving is smaller.
£3.00 + £2.80 + £0.50 (free) = save £0.50
Saving: £0.50 / £6.30 = just 7.9%
vs same-price items: 33.3%
Price per unit is the only fair comparison
To compare any two deals fairly, convert everything to price per item. A £2.50 bottle at 20% off costs £2.00 each. A £1.60 bottle with no deal costs £1.60 each. The "deal" price is still more expensive.
£2.50 - 20% = £2.00/item
£1.60 (no deal) = £1.60/item
Winner: the cheaper bottle
Multi-buy deals: check the unit price
Supermarkets often place multi-buy prices next to single items to make them look cheaper. Always check what you're actually paying per item — the multi-buy isn't always the better deal.
3 for £5.00 = £1.67/item
Single price = £1.80/item
Multi-buy saves 7.2% — worth it?