How Stacked Discounts Really Work: 30% + 20% Is Not 50%

Successive percentages multiply

A “30% off, plus an extra 20% off at checkout” sale takes 30% off first, then 20% off the already-reduced price. You pay 70% × 80% = 56% of the original, which is 44% off — not 50%.

The general rule: multiply the remaining fractions. Three stacked discounts of 10%, 20% and 25% leave 0.9 × 0.8 × 0.75 = 54% of the price, or 46% off.

Order matters when a coupon is a fixed amount

On a $100 item with a 20% discount and a $10 coupon, the order of the two changes the price:

• 20% off first, then $10 off: $80 − $10 = $70.
• $10 off first, then 20% off: $90 × 0.8 = $72.

The fixed coupon is worth more when it comes last. Stores decide the order, so read the receipt; if a cashier can choose, ask for percentages first.

Multi-buy offers

• “Buy one, get one 50% off” on two equal items is 25% off each — you pay 1.5 prices for 2.
• “Buy 2, get 1 free” is 33.3% off each — but only if you wanted three.
• “Buy one, get one free” is 50% off each, the only multi-buy that matches its headline.
• “Spend $100, save $20” is 20% off at exactly $100 and less above it: at $130 it is 15.4%.

Discounts and sales tax

Store discounts are applied before sales tax, so tax is charged on the lower price — the discount also saves you tax. An $80 item at 25% off is $60; with 8% sales tax you pay $64.80 rather than $86.40. Manufacturer coupons can be treated differently: in some states tax is charged on the price before the manufacturer’s coupon, because the store is reimbursed for it.

Is it really a deal?

• Check the reference price. A “was” price the item rarely sold at, or a list price raised just before a sale, inflates the percentage. Price-history tools show what an item actually cost last month.
• “Up to 70% off” describes the best item in the sale, not the typical one.
• Compare unit prices for multi-packs and “bonus size” offers: 40% more product is a 28.6% saving per unit, not 40%.
• Subscriptions: compare the discounted first period with the full price you will pay afterwards.
• Shipping thresholds: adding a $15 item to reach free shipping only saves money if you wanted the item.

The discount calculator shows the sale price and saving for any price and percentage, and the percentage calculator works out the percentage change between two prices.

Working backwards from a sale price

To find the original price from a sale price, divide by the fraction you paid: original = sale ÷ (1 − discount). A $59.99 item at 25% off was originally $79.99; a $45 item at 40% off was $75. To find the discount between two prices, divide the saving by the original price — the percentage calculator’s percentage-change section does this directly.

Percent versus percentage points

When a sale goes from 20% off to 30% off, the discount rose by 10 percentage points, but the saving grew by 50% (from 20 to 30). On a $100 item, you pay $80 versus $70 — 12.5% less than before. Advertisements and price-comparison sites mix these terms freely; translating everything back into what you pay is the only reliable comparison.

Price adjustments and coupon policies

• Price adjustments: some retailers refund the difference if an item you bought goes on sale within a set period. Keep receipts and check the window.
• Coupon stacking: many stores allow one store coupon plus one manufacturer coupon per item, but not two store coupons. Policies are usually published on the store’s website.
• Cashback and card rewards are calculated on what you actually pay after discounts and before or after tax depending on the programme.
• Loyalty “points” are only worth their redemption value. Divide the reward by the spend required to see the real percentage back.

A full checkout, step by step

A $120 jacket is 30% off, the store adds an extra 15% at checkout, you have a $10 coupon, and sales tax is 8%. In order: $120 × 0.70 = $84.00, then × 0.85 = $71.40, then − $10 = $61.40, then + 8% tax = $66.31. Before tax, the combined discount is 48.8% — well short of the “30 + 15 + coupon” that sounds like more than half off. Running each step through the discount calculator takes seconds and removes the guesswork.

Timing purchases

• Clearance cycles: seasonal goods are usually discounted most at the end of the season, when stores need the space.
• Big sale events can include items whose price was raised beforehand; compare with the price a few weeks earlier.
• Some retailers send discounts to customers who leave items in a basket — useful for considered purchases, not for impulse buys.

Reading unit prices

Shelf labels in many stores show a unit price — per ounce, per 100 grams or per item — next to the total. It is the quickest way to compare a sale on one size with the regular price of another. A 24-pack at 20% off can still cost more per can than a 36-pack at full price; dividing the price by the quantity takes a few seconds and settles it. Remember that the cheapest unit price only saves money if you will use the whole quantity before it expires.