Percentage-off formula, stacked discounts, buy-one-get-one math, and how to calculate the final price when multiple promotions apply at checkout.
A discount is a reduction from an original price, usually expressed as a percentage. When a retailer marks an item down, the percentage tells you how much of the original price is removed, and the sale price is what remains. Understanding this relationship lets you judge whether a "huge discount" is actually a good deal or just a markdown from an inflated starting price.
The key distinction is between the discount amount — the dollars you save — and the sale price — the dollars you pay. A 30% discount sounds large, but its value depends entirely on the original price. Thirty percent off a $10 item saves $3; thirty percent off a $500 item saves $150. The percentage is the same, but the dollar impact is very different, which is why converting percentages to dollars is the essential shopping skill.
Retailers also use discounts strategically. A markdown clears inventory and can pull in price-sensitive shoppers, but it compresses profit margins. For the shopper, the goal is to compare the final sale price — including any tax — against the item's value to you, not against the original price, which may have been set high precisely to make the discount look more attractive.
Calculating a discount comes down to two simple formulas. The first finds the dollar amount of the discount; the second finds the sale price directly from the original price and the discount percentage.
Discount = Original Price × (Discount % ÷ 100) Sale Price = Original Price × (1 − Discount % ÷ 100)
For example, a $50 item at 30% off gives a discount of $50 × 0.30 = $15 and a sale price of $50 × (1 − 0.30) = $35. A useful mental shortcut for common percentages: 10% is just moving the decimal one place left ($5 here), and 20% is double that ($10), so 30% is triple ($15). The Metriova discount calculator handles these conversions instantly and works for any percentage, including awkward ones like 17% or 33%.
When sales tax applies, it is calculated on the sale price, not the original price. So a $50 item marked down to $35 in a jurisdiction with 8% tax costs $35 × 1.08 = $37.80, not $50 × 1.08. Applying tax to the discounted price is one of the most common small errors people make when estimating a total at the register.
Retail discounts come in several patterns, and the math differs subtly for each. The table below shows how a few common discount types translate into final prices on a $100 original.
| Discount type | Final price on a $100 item |
|---|---|
| Single 20% off | $80 |
| Single 30% off | $70 |
| BOGO 50% off (buy one, get one half off) | $75 average per item |
| Two stacked discounts: 20% then 10% | $72 (28% effective) |
| "$20 off $100" coupon | $80 |
Notice that two stacked discounts of 20% and 10% do not equal a 30% discount. Applying them in sequence gives $100 × 0.80 × 0.90 = $72, an effective discount of 28%, not 30%. Stacked percentages always compound multiplicatively, so the combined reduction is smaller than the simple sum of the two percentages. This is why retailers love advertising "an extra 10% off already-reduced prices" — the true additional saving is less than shoppers assume.
Fixed-dollar coupons behave differently from percentage discounts. A "$20 off $100" coupon saves exactly $20 regardless of the price, so it is more valuable on lower-priced items (where $20 is a larger share) and less valuable on expensive ones. When a store offers both a percentage-off sale and a fixed-dollar coupon, compare the two outcomes rather than assuming one is always better.
A few habits turn discount math into real savings. The objective is not to maximize the percentage you save, but to minimize what you spend on things you actually need.
Finally, a discount only saves money if you were going to buy the item anyway. Marketers design promotions to trigger purchases that would not otherwise happen, converting a "saving" into spending. Running the numbers before you reach the register — original price, discount percent, sale price, and tax — is the simplest way to keep discounts working in your favor rather than against you.
Discount Calculator — Sale Price & Stacked Savings
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