About PercentLab
PercentLab is a free calculator that brings together the percentage calculations you meet most often in daily life and at work. Results update the moment you type, and below each result you see exactly how it was calculated. It is built so you can check the math instead of just trusting the answer.
Every calculation runs inside the browser you are using. The amounts and rates you enter are never sent to a server or stored.
Key features
- Five percentage basics — B% of A, A is what % of B, percent change from A to B, a value increased (decreased) by B%, and the original value worked back from a changed value
- Discount calculator — sale price and savings from the original price and discount rate, with the effective rate of stacked discounts applied one after another
- VAT calculator — net → gross, and gross → net with the tax split out. Presets for 49 countries, with truncate/round/round-up options for the tax amount
- Margin & markup — margin and markup at once from cost and price, selling price from a target margin or markup, and conversion between the two
- Percentage points (%p) — compare the %p difference and the relative change (%) of two rates side by side
- Steps & copy — every result shows its formula and can be copied with one click
How to use
- Pick a calculation type (Percent, Discount, VAT, Margin, %p) from the tabs at the top.
- Type numbers into the fields and the result appears immediately. Thousands separators (1,000) are fine.
- Use Decimals at the top right to set how many decimal places are shown. For amounts, the Amount rounding option in the Discount and VAT tabs lets you round to the cent, to whole units and so on.
- Use the Copy button next to a result to copy it to the clipboard. Bookmark a tab address (e.g. /#vat) to open that calculator directly.
Frequently asked questions
If I use a 20% off coupon plus an extra 10% off, is that 30% off?
No. The second discount applies to the already-discounted price, so 0.8 × 0.9 = 0.72 and the actual discount is 28%. Enter several rates in the Discount tab to see the actual rate and how it differs from the simple sum.
How do I get the net amount from a VAT-inclusive total?
At a 10% rate, the net amount is total ÷ 1.1 and the VAT is total − net. Taking 10% off the total (total × 0.9) is the wrong method.
Won't a calculation like 0.1 + 0.2 show 0.30000000000000004?
No. Errors caused by the computer's binary floating-point representation are cleaned up at 12 significant digits before rounding, so the result shows as 0.3. Rounding 1.005 to two decimal places gives 1.01.
What is the difference between margin and markup?
Both express profit as a ratio, but with a different denominator. Margin is profit ÷ selling price; markup is profit ÷ cost. With a cost of 70 and a price of 100, the margin is 30% and the markup is about 42.86%.
How is % different from %p (percentage points)?
If an interest rate rises from 3% to 4%, the difference is 1 percentage point, and in relative terms it rose 33.3%. %p is a subtraction between rates; % is the ratio of the change.
How accurate are the country tax rates?
The rates page lists its reference date and sources. Rates can change with new legislation and there are reduced rates and exemptions for specific goods, so for filings, contracts and other official uses, check the latest guidance from that country's tax authority.