Tools that show their working.

Free calculators for everyday questions, from percentages to prayer times. Nothing to sign up for, and nothing you type leaves your browser.

Browse by category

Muslim tools
Calculators and reference tools for prayer, fasting and zakat, each one showing the method it follows and the choices it leaves to you.
42 tools
Calculators
Percentages, changes and totals, worked out in one step and shown with the figures behind them.
1 tool
Finance & money
Loans, compound growth, savings goals, discounts and margins. Each tool shows the formula it applied and names what it does not model.
5 tools
Date & time
Ages, gaps between dates, shifting a date forward or back, hours between two times, and countdowns. All worked on the ordinary Gregorian calendar.
6 tools
Developer tools
Formatting, encoding and decoding the things you paste between one window and another. All of it runs in your own browser, and nothing is uploaded.
6 tools
Text & writing
Counting, cleaning, recasing and slugging a block of text. Every one is instant, and every one runs in your own browser.
7 tools
Business & freelancing
Setting a rate, pricing a job, splitting a commission and finding the point a business starts making money. Each tool shows the assumptions it ran on.
8 tools
Image & file tools
Compressing, resizing, converting and combining images, plus the arithmetic of file sizes. Every one runs in your own browser, and nothing is uploaded.
8 tools
Everyday utilities
Converting between the units people meet in ordinary life: centimetres and inches, kilograms and pounds, Celsius and Fahrenheit. Every figure is exact where the definition is.
5 tools
Pakistan tools
Tools built around rules that only apply in Pakistan: the 200-unit electricity threshold, what an instalment plan really costs, and what a freelance invoice is worth once it reaches a rupee account.
5 tools

A few to start with

Prayer times calculator

The five daily prayer times for any place and date

London, 21 JuneSunrise 04:43

Percentage calculator

Percentages, increases and reverse totals

Finance & money

Loan / EMI calculator

The monthly payment, and what it costs in total

$20,000 over 5 years at 7%$396.02 a month

Age calculator

Your exact age, and when the next birthday lands

15 March 1994 to 1 January 202732 years, 9 months and 17 days

Developer tools

JSON formatter & validator

Indent it, shrink it, or find out what is wrong with it

{"b":1,"a":[2,3]}Formatted, 2-space indent

Word counter

Words, sentences, paragraphs and how long it takes to read

A 500-word essayAbout 2 minutes to read

Business & freelancing

Hourly rate calculator

What to charge, once the unbillable hours are counted

$60,000 take-home, $6,000 costs, 20% tax$67.50 over 1,200 billable hours

Image & file tools

Image compressor

Fewer bytes, same picture, nothing uploaded

A 4 MB photo at 70% qualitySame dimensions, a fraction of the bytes

Everyday utilities

Unit converter

Seven kinds of measurement, one page

1 US gallon in litres3.785411784 L

200-unit electricity guard

Whether this month crosses the protected limit

120 units, 15 days in, 15 to goOn course for 240 units

How these tools work

Nothing leaves your browser: Calculations run on your own device. The figures you type are never uploaded, stored or logged, and closing the tab clears them.
The working is shown: Every result lists the figures behind it, so you can check the answer instead of taking it on trust.
Assumptions are stated: Where a calculation rests on a disputed rule or a price that moves, the tool says so and lets you set it yourself.