Percentage calculator

Work out a percentage of a number, percentage change, markup and margin in one calculator. Every result comes with the formula spelled out.

How to calculate a percentage

1
Pick the calculation you need
Choose from six modes: percentage of a number, what percent one number is of another, percentage change, adding or subtracting a percentage, reverse percentage, or markup versus margin.
2
Enter the two numbers
Type both values. Commas and dots both work as a decimal separator, and spaces used as thousand separators are ignored.
3
Read the result and the formula
The answer appears immediately, along with a plain-language sentence spelling out exactly how it was calculated.

Markup vs. margin, the mix-up this tool exists to fix

Markup and margin both compare the same two numbers, cost and price, but from different starting points, and that difference matters for pricing decisions. Markup is the price increase measured against cost: sell something that cost $80 for $100 and the markup is 25%. Margin is the same $20 difference measured against the price instead: on that $100 sale, margin is 20%. They are never the same number except at 0%, which is exactly why this calculator always shows both side by side.

Why percentage change uses the absolute value of the starting number

Percentage change divides the difference by the absolute value of the starting number rather than the plain starting number. Without that, a change starting from a negative figure would flip sign in a way that reads backwards. A temperature moving from -10 to -5 is a genuine increase, and using the absolute value keeps the reported percentage positive and readable instead of technically correct but confusing.

Your numbers never leave this tab

Every calculation on this page runs in JavaScript in your browser the moment you type. There is no upload and no server involved; analytics only records which calculation mode was used, never the numbers themselves.

Frequently asked questions

What is the difference between markup and margin?

Markup is calculated against cost: (price minus cost) divided by cost. Margin is calculated against price: (price minus cost) divided by price. The same $20 profit on an $80 cost gives a 25% markup but only a 20% margin, because the two formulas divide by different numbers.

How do you calculate percentage change from a negative number?

The difference between the two numbers is divided by the absolute value of the starting number, not the number itself. This keeps the sign of the result matching common sense: moving from -100 to -50 is reported as a 50% increase, not a confusing negative-over-negative figure.

Why is percentage change from zero undefined?

Percentage change is a ratio of the difference to the starting value, and dividing by zero has no defined answer. If your starting point is genuinely zero, describe the change in absolute terms instead of a percentage.

How do I add sales tax to a price?

Use the add-or-subtract mode: enter the price as the first number, the tax rate as the percentage, and choose add. The result is the price including tax, and the formula sentence underneath shows the exact calculation.

How many decimal places does the result use?

Two by default, adjustable from 0 to 6 in the options panel. Trailing zeros are dropped, so a result that only needs one decimal place is not padded with extra zeros.

Can I share a specific calculation with someone else?

Each mode has its own dedicated page. The percentage-of, percentage-change and markup-vs-margin pages linked from this calculator open with that mode already selected, ready for your two numbers.

Does this send my numbers to a server?

No. Both numbers are read straight from the form and every formula runs locally in your browser. Nothing about the values you enter is uploaded or stored.