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Every Date and Age Calculator in One Place

Start with the scientific calculator below, then pick a calculator for the calendar question you actually came for, exact age, days between two dates, working days, due dates and more. Everything runs in your browser and nothing you type is sent anywhere.

Scientific calculator
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The conventions every calculator here follows

Date arithmetic looks like it should have one answer. It does not. Ask two competent people how many days lie between 1 March and 3 March and one will say two while the other says three, and both are right, they are answering slightly different questions. Almost every disagreement between two date calculators comes down to a convention that neither tool bothered to state.

So here are the five decisions this site makes, in one place, applying to all calculators. If you ever get a figure that differs from another tool, the cause will be in this table.

Decision What we do Why
Months and years Whole calendar units, counted in order Matches how ages and notice periods are written on official paperwork; averaging a month to 30.44 days does not
Both endpoints Exclusive by default, with the inclusive count shown alongside where it matters Subtraction is what a computer does; inclusive counting is what hire agreements and notice periods mean
Time of day Both dates normalised to midnight before subtracting Stops a daylight-saving change from silently adding or removing a day from a long span
Dates on the 31st A month only completes if the target month has that day number The conservative reading, and the one a registrar applies, clamping instead advances the month counter a day early
Leap days Counted like any other day, always Real calendar days are what a diary shows; 365-a-year estimates drift by a day every four years

Every calculator page repeats the rule that applies to it, so you never have to come back here to check.

Where to start

If you came here to find out how old you are, the age calculator gives your exact age in years, months and days plus the same span in months, weeks, days and hours. If you have two dates rather than a birthday, the date difference calculator is the one you want, and for deadlines that only count business days there is the working days calculator. The full set, with a table matching questions to tools, is on the calculators page.

About the scientific calculator at the top

The keypad above handles everyday arithmetic as well as powers, roots, logarithms, trigonometry, factorials, percentages, parentheses and memory. Use the Deg and Rad controls to choose how trigonometric angles are interpreted.

Expressions follow standard mathematical precedence. For example, 2 + 3 × 4 returns 14, while parentheses let you make (2 + 3) × 4 return 20. The Ans key recalls the previous result, and the memory keys keep a separate value while you work through another calculation.

Scientific functions

The trigonometric keys include sine, cosine, tangent and their inverse functions. You can also calculate square and cube powers, arbitrary powers and roots, natural and base-ten logarithms, reciprocals and factorials. Invalid operations, such as dividing by zero or taking the square root of a negative number, show Error.

Keyboard shortcuts

Click any key once and the keypad takes keyboard input: digits and . type numbers, + - * / set the operation, parentheses group an expression, Enter is equals, Backspace deletes the last digit and Esc clears everything. x works as multiply and a comma works as a decimal point.

Percent divides whatever is on screen by a hundred. That makes 250 × 20 % give 50, and 250 + 20 % give 250.2 rather than 300, the second is the honest reading of the keys you pressed, and it is where percent keys on cheap calculators quietly disagree with one another. If you want a percentage of something, multiply.

Built to be quick, private and honest

Nothing leaves your browser

Every calculation happens on your device in JavaScript. No dates are uploaded, logged or stored, there is no server-side calculator here to send them to.

No sign-up, no paywall

No account, no trial. Open a tool, enter a date, read the answer. The pages are static HTML, so they load fast on a slow connection too.

The method is written down

Each calculator explains its convention, inclusive or exclusive day counts, how month-ends are clamped, which reference table it uses. If you disagree with a choice, you can at least see it.

Frequently Asked Questions

What can I work out on this site?
The tools fall into two useful groups. Date calculators cover exact age, gaps between dates, shifted dates, working days and birthday countdowns. Life calculators cover retirement timing, due dates, zodiac and birthstone lookups, generations, dog years and half birthdays. The calculator at the top of this page handles everyday scientific arithmetic.
Is anything I type sent to a server?
No. Every calculator here is client-side JavaScript. The date or number you enter is read by the page, used for the arithmetic, and discarded when you close the tab. There is no server-side calculator to send it to, no account to create and no database storing results. Our Privacy Policy sets out what the site does collect, advertising and analytics cookies, and how to control it.
Why do two date calculators sometimes give different answers?
Almost always because of a convention rather than a bug. The three that matter most are whether both endpoints are counted (1 March to 3 March is either 2 days or 3), whether a month means a calendar month or an average of 30.44 days, and how a date on the 31st is handled in a month that has only 30. Every calculator on this site names the convention it uses on its own page, so you can tell which of the two correct answers you are being given.
Do the calculators handle leap years and 29 February?
Yes. The maths runs on real calendar dates rather than a fixed 365-day year, so every 29 February inside a span is counted automatically. That is why a total-day figure rarely equals age × 365, the difference is exactly the number of leap days involved. For a birthday that falls on 29 February the tools use 28 February in ordinary years, the convention most administrative software follows; the leap-day guide explains where the law differs.
Does my time zone affect the result?
No. Both dates are normalised to midnight before subtracting, so a daylight-saving change or a browser set to another time zone cannot shift an answer by a day. This is a genuine failure mode in naive date code, subtracting two timestamps can lose an hour to a clock change and report 89 days where the answer is 90, and it is the reason day counts here are computed from calendar dates rather than milliseconds.
Can I use these results for official or legal purposes?
The arithmetic is precise and you are welcome to use it as a working figure. But dates and ages carry legal consequences, eligibility, notice periods, entitlements, and the rules vary by country. Treat every result as a reliable calculation, not as legal, medical or financial advice. Our Disclaimer says this plainly, and each calculator page explains the assumptions behind its own numbers.