Percentage calculator
Eight percentage calculations with the formula explained, including the ones people usually get wrong: chained discounts, original value and margin versus markup.
Result
12
Remainder
68
Sum
92
How it is calculated
80 × 15 / 100 = 12
Built by
Miguel Ángel Colorado Marin (MACM)
Built by
Miguel Ángel Colorado Marin (MACM)
Full-Stack Developer · Guadalajara, España
I develop web apps, digital tools and full projects — from design to deployment.
Percentages look simple until they are chained. A 20% discount followed by another 10% is not 30% but 28%; raising a price by 20% and then cutting it by 20% does not leave it unchanged; and taking 21% off a VAT-inclusive price does not give back the net amount. This calculator solves the eight common cases and shows the formula applied to your numbers so you can check it. It also separates margin on the sale price from markup on cost, a mix-up that leads to underpricing, and percentage points from relative change.
Features
- ✓Eight modes: % of a number, what % is, change, increase or decrease, original value, chained, margin and percentage points
- ✓Step-by-step formula with your numbers to understand and check the result
- ✓Chained discounts with the equivalent single percentage and the naive sum you should not use
- ✓Original value before an increase or discount, warning about the common mistake of subtracting the %
- ✓Margin on sales versus markup on cost and conversion between them
- ✓Difference between percentage points and relative change
- ✓Accepts Spanish (1.234,56) and English (1,234.56) number formats and 0 to 8 decimals
- ✓Local history of copied results, nothing is sent to any server
How do I calculate a percentage?
- 1
Pick the calculation
Select one of the eight modes, from the % of a number to profit margin.
- 2
Fill in the sentence
Type the numbers into the question; you can use a decimal comma or point.
- 3
Review the formula
The result updates instantly with the step-by-step operation and extra figures.
- 4
Adjust and copy
Choose how many decimals you want and copy the result; it is kept in your local history.
Frequently asked questions
How do you calculate the percentage of a number?
Multiply the number by the percentage and divide by 100. For example, 15% of 80 is 80 × 15 / 100 = 12.
Why don't 20% and 10% discounts add up to 30%?
Because the second discount applies to the already reduced price. 100 × 0.80 × 0.90 = 72, a total discount of 28%. The calculator shows the equivalent single percentage for any chain.
How do I get the original price before a discount or increase?
Divide the final value by the factor: original = final / (1 ± p/100). If a product costs 121 with 21% included, the original is 121 / 1.21 = 100. Subtracting 21% from 121 would give 95.59, which is wrong.
What is the difference between margin and markup?
Margin is calculated on the sale price and markup on cost. Buying at 60 and selling at 100 is a 40% margin but a 66.67% markup. If you want a 40% margin and apply a 40% markup to cost, you will sell at 84 instead of 100.
What are percentage points?
They are the direct difference between two percentages. Going from 10% to 12% is a 2 percentage point rise but a 20% relative change. Mixing them up is common in news about interest or unemployment rates.
Why is there no percentage change from zero?
Because it would require dividing by zero: going from 0 to any amount is an infinite relative increase. In that case the calculator shows a warning instead of a misleading number.
Related tools
Embed Percentage Calculator on your site
Add Percentage Calculator to any web page with a simple iframe. Free, with attribution to miguelacm.es.
<iframe
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width="100%"
height="700"
frameborder="0"
title="Percentage Calculator — miguelacm.es"
></iframe>