commerce calculator
Discount Calculator
Calculate sale prices, savings, original prices, discount rates, successive discounts, tax estimates, and quantity totals.
7 pricing modes
Calculate discounts and sale prices
Result
Enter pricing details and choose Calculate.
Formula version 1.0.0 · Currency-neutral; tax is applied after discount.
Transparent pricing
Discount formulas and worked examples
The calculator is currency-neutral. Keep every amount in the same currency; displayed rounding does not change the underlying result.
Sale price and savings
sale = original × (1 − discount/100)
savings = original − sale. Example: 20% off 80 gives 64, saving 16.
Original price and discount rate
original = sale/(1 − discount/100)
discount% = (original − sale)/original × 100
Successive discounts
final = original(1−d₁)(1−d₂). Discounts add multiplicatively, not arithmetically.
20% then 10% gives an effective 28% discount.
Tax after discount
tax = discounted price × tax rate. Local rules may use a different taxable base.
How to use this calculator
- Choose the needed Calculation type: price, savings, original price, discount percentage, successive discounts, discount then tax, or quantity total.
- Complete every displayed field using one currency for all price amounts.
- Enter percentages without the percent sign; Quantity must be a whole nonnegative number.
- Select Calculate, then read Result, Sale price, Savings, Effective discount, and any Tax added after discount.
Symbols and units
| Symbol | Meaning | Unit or domain |
|---|---|---|
P | Original price before discount | Any one consistent currency |
S | Sale price after discount and before any tax | Same currency as P |
d | Discount percentage divided by 100 when used as a multiplier | Decimal rate |
d₁, d₂ | First and second successive discount rates | Decimal rates |
t | Tax-after-discount percentage divided by 100 | Decimal rate |
q | Whole-number quantity | Item count |
Savings | Original price minus sale price | Same currency as P |
Checked examples
Sale price and savings
Inputs: Calculation type: Price after discount; Original price: 75.80; Discount (%): 25
Calculation: Sale price = 75.80 × (1 − 25/100) = 56.85; savings = 75.80 − 56.85
Result: Sale price 56.85; savings 18.95
The item costs 56.85 in the same currency, before any tax or fee not entered.
Check: discount-general.test.ts — calculates price and savings
Two successive discounts
Inputs: Calculation type: Two successive discounts; Original price: 245; Discount (%): 20; Second discount (%): 12
Calculation: 245 × 0.80 × 0.88 = 172.48; effective discount = 1 − (0.80×0.88) = 29.6%
Result: 172.48 with an effective discount of 29.6%
Successive discounts multiply; 20% and 12% do not add to 32%.
Check: discount-general.test.ts — applies successive discounts multiplicatively
Discount followed by tax
Inputs: Calculation type: Discount then tax; Original price: 80; Discount (%): 30; Tax after discount (%): 10
Calculation: Discounted price = 80×0.70 = 56; tax = 56×0.10 = 5.60; total = 61.60
Result: 61.60; tax amount 5.60
The model applies tax to the discounted price; local taxable-base rules may differ.
Check: discount-general.test.ts — applies tax after discount
Assumptions, rounding, and limits
- All price fields are nonnegative finite amounts in one consistent currency; the calculator does not convert currencies.
- Percentage inputs are interpreted as rates, such as 20 for 20%; supported domain limits are enforced by the formula.
- Original-price recovery is undefined at a 100% discount because division by zero would be required.
- Discount-rate mode requires an original price greater than zero.
- Successive discounts are applied multiplicatively, not added.
- Tax mode applies the entered rate after discount. It does not determine jurisdiction, taxable base, exemptions, fees, or official tax liability.
- Quantity must be a whole nonnegative count; the quantity mode multiplies the discounted unit price by that count.
- The formula keeps working precision; price results display to two decimal places and effective discount to four decimal places using half-up display formatting.
- Results are educational estimates, not a merchant quote, invoice, tax determination, or guarantee that a promotion applies.
Frequently asked questions
Why do two discounts not add together?
The second discount applies to the already-discounted price. For example, 20% then 10% leaves 0.80×0.90 = 0.72 of the original price, an effective 28% discount.
Does this calculator include sales tax or VAT?
Only Discount then tax uses a tax rate, and it applies that rate to the discounted price. Local rules, exemptions, fees, and rounding may use a different taxable base.
Why can’t I recover an original price from a 100% discount?
A 100% discount makes every original price produce a zero sale price, so the original cannot be uniquely recovered by division.
Sources and review
- OpenStax: Discounts, Markups, and Sales Tax — Accessed 2026-10-25
- GOV.UK: VAT on discounts and gifts — Accessed 2026-10-25
- Formula version
- discount.general@1.0.0
- Formula review
- Formula review: Equatara formula review
- Editorial review
- Editorial review: Equatara editorial review
- Last verified
- 2026-10-25
- Applicability
- Global currency-neutral discount mathematics; tax treatment is only the stated after-discount model
- Next review
- On material formula/source change, or by 2028-10-25.
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