Five everyday calculations
X% of a number answers questions like "what is 15% of 80?", useful for a tip, a commission or a down payment. "What percent one number is of another" tells you, for example, that 18 correct answers out of 24 is 75%, or what share of the monthly budget goes to rent.
Percentage change compares a starting value with a final one and says how much it increased or decreased, which is what you need to compare prices from one month to the next, the growth of sales or followers, or the change in a utility bill. Add or subtract a percentage gives the final number directly: a price after a 20% discount, a salary after a 4% raise or a quote with a 10% margin.
Sales tax and VAT
The tax mode adds tax to a price or removes it from a price that already includes it, and shows three figures: the amount before tax, the tax and the total. That is handy for invoices, quotes, receipts and price lists, and for checking what part of a price is tax.
It includes the standard rates of Mexico (16%), Colombia (19%), Spain (21%), Portugal (23%), Argentina (21%), Chile (19%) and Peru (IGV, 18%), plus "Other rate" for any percentage you type. In the United States there is no national sales tax: the rate depends on the state and often the city or county, so enter your local rate as "Other rate". Some goods have reduced rates or are exempt, so confirm the right rate for your product. The VAT calculator page starts directly in this mode.
Common mistakes it avoids
Removing tax is not the same as subtracting the percentage. If a price of 121 includes 21% VAT, the price before tax is 100, not 95.59, because the 21% was calculated on 100. The calculator divides correctly, so the amounts on an invoice add up.
In the same way, a 20% increase followed by a 20% decrease does not bring you back to the start. The percentage change mode shows the real difference between two values, so you don't have to guess.
Fast and private
There is no button to press: the result updates while you type. Everything is calculated in your browser, so your numbers are not sent anywhere. It is free, with no account, on phones and computers.
To write an amount in words for a check or an invoice, use Number to words, and to count days between two dates, Date calculator.