Percentage Calculator

About this percentage calculator

Five tabs cover the percentage questions that come up most often: what is P% of a value, what percent one number is of another, percent change between two numbers, recovering an original value before a discount or markup, and the gap between margin and markup. It also makes three commonly confused distinctions explicit on screen — percentage points versus percent change, the asymmetry of a drop and the gain needed to recover it, and margin versus markup.

How it works

Every calculation is plain arithmetic that runs in your browser on each keystroke — there is no server round-trip and nothing you type is uploaded. Percent change is (B − A) / A × 100. The gain needed to recover from a d% drop is d / (1 − d), which is why a 50% drop needs a 100% gain, not another 50%. A reverse discount divides rather than multiplies: 80 after 20% off is 80 ÷ 0.8 = 100. Markup divides profit by cost; margin divides profit by price.

Notes & conventions

Results are rounded half-up to at most four decimal places, with trailing zeros trimmed. Inputs accept a leading $, percent signs, and thousands separators, all of which are stripped before calculating; a percent field is read as the number you type (15 means 15%). Divide-by-zero cases — a zero total, a zero base, a 100%-off reverse, or a target margin of 100% or more — show an inline error instead of a number.

FAQ

What is the difference between a percentage point and a percent?

Going from 4% to 5% is a rise of one percentage point, but a 25% relative increase (1 ÷ 4). Use percentage points for the absolute gap between two rates, and percent change for how much one rate grew relative to the other. A drop from 50% to 40% is 10 percentage points, or a 20% relative decline.

How do I find the original price before a discount?

Divide, do not multiply. An item that costs 80 after 20% off has an original price of 80 ÷ (1 − 0.20) = 100, not 80 × 1.2 = 96. The Reverse tab does this division and also shows the common multiply mistake for contrast.

Is markup the same as margin?

No. Markup divides profit by cost; margin divides profit by price. For a cost of 40 and a price of 100 the same 60 profit is a 150% markup but a 60% margin.