Discounts, Offers and "Buy 2 Get 1" Maths

How stacked discounts, cashback and multi-buy offers really work, why 20 percent plus 10 percent isn't 30 percent, and how to find the true saving.

Shops and apps use many kinds of offers. Doing the maths reveals what you actually save.

Stacked discounts

A shirt costs 1,000 rupees, with 20 percent off plus an extra 10 percent off.

After 20 percent: 800 rupees.
Extra 10 percent is on 800: 80 rupees off, so 720 rupees.

Total saving: 280 rupees, or 28 percent, not 30 percent. The second discount applies to the already-reduced price.

“Up to” offers

“Up to 70 percent off” means only some items have 70 percent off; many may have much smaller discounts.

Buy 2 get 1 free

If each item costs 300 rupees and you get three for 600, the discount is 300 / 900 = 33 percent per item. But it’s only a saving if you need three. If you need one, you pay 600 instead of 300.

Cashback

“10 percent cashback up to 100 rupees” on a 2,000 rupee purchase gives only 100 rupees back, a 5 percent saving. Cashback may also come as store credit or points with expiry dates, which are worth less than cash.

Percentage off vs flat amount

Which is better on a 1,500 rupee item: 15 percent off or 200 rupees off? 15 percent of 1,500 is 225 rupees, so the percentage offer wins. On a 1,000 rupee item, 15 percent is 150 rupees, so the flat 200 is better.

Taxes and delivery

Check whether taxes, delivery fees or convenience charges are added after discounts. A cheap product with high delivery charges may cost more than a slightly pricier one with free delivery.

Inflated “original” prices

Some sellers show a high “was” price to make discounts look bigger. Compare the final price with other shops, not with the stated original price.

Two apps

One app offers a phone at 20,000 rupees with 10 percent bank cashback up to 1,500. Another offers it at 19,200 with no cashback. The first gives a saving of just 1,500 (capped), so the effective price is 18,500. The first app wins, if the cashback is actually credited.

Thinking stacked discounts simply add up

Each discount applies to the reduced price, so 20 percent plus 10 percent is 28 percent, not 30.

Key takeaways

Stacked discounts multiply rather than add: 20 plus 10 percent equals 28 percent.
Multi-buy offers save money only if you need the extra items.
Cashback caps and conditions reduce the real saving.
Compare final prices, including taxes and delivery, across sellers.