How to calculate discounts: formula, examples, and free calculator
Learn to calculate percentage discounts, stacked discounts, final price with tax, and smart shopping tricks. Free online discount calculator.
The basic discount formula: how it works
Calculating a discount is simple math that many people get wrong mentally. The basic formula is:
Final price = Original price × (1 - discount/100)
Example: A product costs $80 with 25% off:
- Discount amount: $80 × 0.25 = $20
- Final price: $80 - $20 = $60
- Or directly: $80 × 0.75 = $60
Quick mental trick: For 10% of any number, move the decimal one place left. $80 → $8 is 10%. For 20%, double it: $16. For 25%, divide by 4: $20.
Calculate any discount instantly with the NexTools discount calculator.
Stacked discounts: why 20% + 20% is not 40%
One of the most common mistakes is believing successive discounts add up. They don't:
Example: $100 product with 20% off + extra 20%:
- First discount: $100 × 0.80 = $80
- Second discount (on $80): $80 × 0.80 = $64
The result is $64, not $60 (which would be 40% off). The difference is $4 and grows with higher prices and discounts.
Stacked discount formula: Final = Price × (1 - d1/100) × (1 - d2/100)
Equivalent single discount: For 20% + 20%: 1 - (0.80 × 0.80) = 36%, not 40%.
Real case: Black Friday "50% off + extra 20% with coupon." Real discount: 1 - (0.50 × 0.80) = 60%, not 70%. Stores know this.
Calculating the original price from the discounted price
Sometimes you need the reverse: if the final price is $60 after 25% off, what was the original?
Formula: Original price = Final price / (1 - discount/100)
$60 / (1 - 0.25) = $60 / 0.75 = $80
Common error: Many calculate $60 + 25% of $60 = $75. This is WRONG because 25% was applied to $80 (original), not $60 (final).
Verify any discount with the NexTools calculator to make sure the advertised discount is real.
Discounts with tax: before or after
Option 1: Discount before tax (common in B2B).
Product: $100, 20% discount, 10% tax:
- Discounted price: $100 × 0.80 = $80
- Tax: $80 × 0.10 = $8
- Total: $88
Option 2: Discount after tax (common in retail).
Product: $100 + 10% tax = $110, 20% discount:
- Total: $110 × 0.80 = $88
Mathematically the result is the same (multiplication is commutative). However, for invoicing the order matters for tax reporting. Use the NexTools percentage calculator for detailed tax calculations.
Types of commercial discounts and how to calculate each
1. Fixed discount. "$10 off purchases over $50." Simple: price - $10. The actual percentage depends on the price.
2. Percentage discount. "30% off." Most common. Standard formula: price × (1 - 0.30).
3. Volume discount. "Buy 3, pay for 2" (effectively 33.3% off). "Second at half price" (25% total on 2 identical items).
4. Early payment discount. Common in B2B: "2/10, n/30" means 2% discount if paid within 10 days. The annualized cost of NOT taking it: (2/98) × (365/20) = 37.24%. Almost always worth taking.
5. Seasonal discount. End-of-season sales typically start at 20-30% and rise to 70% in the final weeks.
6. Coupon discount. Can be percentage or fixed. Some have minimum purchase requirements.
Pricing psychology tricks and how to avoid them
1. Inflated anchor price. "Was $200, now $99 (50% OFF!)." But the product never sold at $200. EU regulations require showing the lowest price from the last 30 days.
2. Discount on discount. "40% + extra 20%" sounds like 60% but is really 52%.
3. "Up to 70% off." The word "up to" does the heavy lifting. Could mean one item has 70% and the rest 10-15%.
4. Prices ending in 9. $99.99 feels significantly less than $100, though the difference is $0.01 (left-digit effect).
5. Minimum purchase for discount. "20% off on purchases over $500." If you only needed $300, spending $200 extra to "save" $100 isn't saving.
Use the NexTools discount calculator before big purchases to know exactly what you're paying.
Discounts in different countries: VAT, tax, and tipping
| Country | Tax rate | Note |
|---|---|---|
| USA | 0-10% sales tax | NOT included in displayed price; varies by state |
| UK | 20% VAT | Included in price; regulated pre-discount pricing |
| Germany | 19% MwSt | Included; VAT refund for non-EU tourists |
| Japan | 10% consumption | Included since 2021; 8% on food |
| Mexico | 16% IVA | Included in displayed price |
| Australia | 10% GST | Included in displayed price |
In the USA, "$50 with 20% OFF" means $40 + sales tax. In the UK, "$50 with 20% OFF" means $40 total.
Calculate tips in any country with the NexTools tip calculator.
Quick formulas for mental discount calculation
10%: Move the decimal. $73 → $7.30
20%: Calculate 10% and double. $73 → $14.60
25%: Divide by 4. $80 → $20
33%: Divide by 3. $90 → $30
50%: Divide by 2.
15%: 10% + half of 10%. $73 → $7.30 + $3.65 = $10.95
75%: Divide by 4 (you pay 25%). $80 → you pay $20
Any other: Decompose. 35% = 30% + 5% = (3 × 10%) + (10%/2).
For exact calculations with decimals, use the NexTools discount calculator.
Try this tool:
Open tool→Frequently asked questions
How do I calculate the final price after a discount
Multiply the original price by (1 - discount/100). Example: $80 with 25% off = $80 × 0.75 = $60. Alternatively: discount = $80 × 0.25 = $20, final price = $80 - $20 = $60.
Why don't two 20% discounts equal 40%
Because the second discount applies to the already-reduced price, not the original. 20% + 20% = 1 - (0.80 × 0.80) = 36%. The gap grows with larger discounts: 50% + 50% = 75%, not 100%.
How can I tell if a discount is real or the price was inflated
Compare prices across multiple stores using price comparison tools (Google Shopping, CamelCamelCamel for Amazon). In the EU, stores must show the lowest price from the last 30 days. In the US, no such regulation exists at the federal level.
Is the discount applied before or after tax
Mathematically the result is the same due to the commutative property. However, for invoicing it matters: B2B typically applies before tax (on the taxable base), retail often applies to the tax-inclusive price.
What does 2/10 n/30 mean in commercial discounts
A B2B payment term: 2% discount if paid within 10 days, full price if paid within 30 days. The annualized cost of not taking it is ~37%, so it's almost always worth paying early.
How do I calculate what percentage discount I'm getting
Formula: Discount % = ((Original - Final) / Original) × 100. Example: original $80, final $60: ((80-60)/80) × 100 = 25%.