Calculators
A calculator should make the answer obvious: a small set of inputs, one prominent result and no reload in between.
TOOLS IN THIS CATEGORY
01 / LISTWHAT YOU CAN DO HERE
02 / OVERVIEWPercentage Calculator covers the four common questions — X% of Y, X is what percent of Y, increase and decrease — and shows the formula it applied. Date Calculator counts whole days between two dates or adds and subtracts days from one. Basic Calculator evaluates a full expression such as (12 + 8) * 3 / 4.
The percentage and date calculators answer one specific question; the basic calculator covers general arithmetic. If you need to convert between number bases instead, that belongs to Number Representations.
- Working out a discount or a tip.
- Counting the days between two dates.
- Doing a quick arithmetic check without opening a spreadsheet.
FREQUENTLY ASKED QUESTIONS
03 / FAQDo calculators need a server?
No. All three compute in the browser tab, and nothing you type is sent anywhere.
What happens when Basic Calculator cannot read an expression?
It shows “Invalid expression” instead of a number. Look for a stray operator, an unbalanced bracket, or a character the parser does not recognise.
Does Date Calculator count the end date?
It returns the difference between the two dates, so 2026-01-01 to 2026-01-02 is 1 day, not 2.