Are Black Friday deals actually cheaper?

Some are, many are not. Investigations by consumer groups repeatedly find that a large share of Black Friday prices were available at the same level or lower earlier in the year. Genuine discounts do exist, particularly on electronics and the retailer's own-brand goods — checking the price history is the only reliable way to tell them apart.

How do I calculate a 20% discount?

Multiply the price by 0.8, or work out 10% by moving the decimal one place and double it, then subtract. A $45 item at 20% off is 45 × 0.8 = $36.

Is 50% off plus 20% off the same as 70% off?

No. The second discount applies to the reduced price, giving 60% off in total. Two stacked discounts always come out lower than their sum.

What is the better deal: 25% off or $25 off?

They break even when the price is $100. Below that, the fixed $25 is worth more; above it, the percentage wins. At $200 the percentage saves you $50.

Is sales tax charged before or after the discount?

After. You only pay tax on the amount you actually spend, so a discount reduces the tax as well.

Discount Calculator – Sale Price & Percent Off

Stacked discounts multiply — they never add

One discountsale = price × (1 − d) Two stacked discountssale = price × (1 − d₁) × (1 − d₂) effective discount = 1 − (1 − d₁)(1 − d₂)

"50% off, plus an extra 20% at checkout" sounds like 70% off. It is 60%. The second discount applies to the already-reduced price, so $100 becomes $50 becomes $40. The gap widens as the discounts grow, and retailers know exactly how appealing the additive misreading is.

Reading a sale honestly

Percentage off what? A discount from an inflated "was" price is not a discount. Many jurisdictions require the reference price to have been genuinely charged for a set period, and enforcement is uneven.
BOGO deals. Buy one get one free is 50% off if you need two items. Buy one get one half price is 25% off. Buy two get one free is 33% off.
Free shipping thresholds. Spending $18 more to save $7 of shipping is not saving $7.
Tax comes last. Tax is charged on the discounted price, so it shrinks with the discount.

How sale pricing is designed to work on you

Discounts are a pricing strategy before they are a saving, and knowing the mechanics makes the arithmetic above more useful.

Anchoring. A crossed-out “was” price exists to make the new price feel like a gain rather than a cost. The anchor works even when shoppers suspect it is inflated.
The rule of 100. Under about $100, a percentage discount feels larger; above it, a fixed amount does. “20% off” on a $30 shirt reads better than “$6 off”, while “$200 off” beats “10% off” on a $2,000 laptop. Same money, different feeling.
Charm pricing. Prices ending in 9 measurably increase sales, apparently because we read left to right and encode $4.99 nearer to $4 than $5.
Artificial urgency. Countdown timers and “only 3 left” badges compress the decision. Many reset on reload.
Threshold spending. Free-shipping minimums reliably raise basket size. Spending $18 more to avoid a $7 charge is a $11 loss.

Two habits neutralise nearly all of it. Decide what the item is worth to you before looking at the discount, and check the price history — on major retailers a browser extension will show whether the “was” price was ever really charged. A genuine 40% off a fair price is a good deal; 40% off an inflated one is full price with extra steps.

When the sale is actually a sale

Discount arithmetic tells you the price. Whether it is a good time to buy is a question of timing and price history.

Predictable annual cycles. Televisions bottom out around late January and late November. Furniture is cheapest in January and July. Clothing is marked down at the end of each season. Laptops fall in late summer and again in late November.
Check the price history. On major retailers a tracking extension will show whether the “was” price was ever really charged. Many headline discounts are measured against a price that existed for a single week.
Price-match and post-purchase adjustment. Many retailers refund the difference if the price drops within two to four weeks. It usually requires asking.
Open-box and refurbished. Manufacturer-refurbished goods with a full warranty are frequently 15–30% cheaper and functionally new.

The only test that matters

Would you buy this at the sale price if there were no discount attached? If yes, the discount is a saving. If no, it is a purchase you did not want at a price you were persuaded by — and 40% off something you will not use is 100% wasted.

Working backwards from the sale price

What percent off is this?discount % = (original − sale) ÷ original × 100 What was the original price?original = sale ÷ (1 − discount)

If a jacket is marked down from $120 to $78, the discount is (120 − 78) ÷ 120 = 35%. If you know a shirt is 40% off at $27, the original was 27 ÷ 0.6 = $45. Both are useful for checking whether the sign on the rack is telling the truth.