About us
Calculators that show their working
We started DailyCalc because most online calculators give you a number and nothing else: no formula, no assumptions and no hint of when the answer stops being reliable. That's fine for a quick sum, but not when the number affects a loan, a notice period or a conversation with your doctor.
So each of our 30calculators comes with the formula it uses, a worked example with realistic numbers, the situations where it's useful and the mistakes people often make. You can check the answer yourself instead of taking it on trust.
Everything is free, nothing needs an account, and the calculations run on your own device. The site is paid for by display ads, which are kept separate from the calculators.
Our principles
How we work
Show the formula
Each calculator shows the exact formula it uses, explains every variable and lists its assumptions, so you can see how a result was reached.
Test the maths
The maths behind each calculator is tested against known correct answers before it goes live, and again whenever we change it.
Explain the limits
Every guide says what the calculator can't do. BMI can't tell muscle from fat, and a loan calculator ignores fees unless you add them. We'd rather say so than leave you guessing.
Keep your numbers private
Calculations run in your browser. The figures you type, such as your salary, weight or date of birth, are never sent to us or stored.
Keep ads separate
The site is paid for by Google AdSense ads, which are kept apart from the calculators. We don't publish sponsored tools or affiliate loan links, and nobody can pay to change a result or a ranking.
Fix mistakes quickly
If you report an error, we check it against the formula and our sources. If we got it wrong, we correct the calculator and its guide and update the date on the page.
How we build a calculator
We start with the standard formula used in that field: the loan repayment formula for EMIs and mortgages, compound interest for savings, the WHO categories for BMI and the Mifflin–St Jeor equation for calorie needs. We then check it against the sources listed on the calculator's page.
Next we decide which inputs to reject. A calculator shouldn't divide by zero, accept a birth date in the future or treat 75 minutes as a valid time, so instead of showing a misleading number it tells you what to fix.
Then we write the guide. We work through an example with realistic numbers, describe the situations people actually use the calculator for, such as a rent review, a night-shift timesheet or a school cut-off date, and list the mistakes we see most often, like adding stacked discounts together or writing 8 hours 25 minutes as 8.25 hours.
Finally, the calculator's correct answers are added to our automated tests, so if a later change breaks a result we find out before it reaches the site. The full process is described in our editorial policy.
By the numbers
- 30
- free calculators
- 4
- categories: math, financial, health, time & date
- 30
- calculators with their sources listed
- 0
- sponsored calculators or paid placements
What we cover
30 calculators in four categories, with more added as readers suggest them.
Start with these
All 30 calculators
BMI Calculator
Know your Body Mass Index in seconds — with healthy-range context.
Open calculator
Percentage Calculator
What is X% of Y? What % is X of Y? Answered with steps.
Open calculator
Percentage Increase / Decrease Calculator
Old → new percent change, with increase vs decrease explained.
Open calculatorThink a result is wrong?
Send us the calculator name, the numbers you entered and the result you expected. We'll check it against the formula and fix the page if we made a mistake.