TetraKits
Find precise age in years, months, and days from any birth date — plus total days lived. Set an optional as-of date to check age on a wedding day, eligibility deadline, or past milestone. The TetraKits Age Calculator runs entirely in your browser — free, private, and ready on mobile or desktop.
Overview
Birthday planning, school enrollment, insurance forms, and genealogy research all need age stated precisely — not just whole years. Enter a birth date and optional reference date to get years, months, days, and total days in one step.
How to use the age calculator
- Enter birth date — Pick the date of birth using the date picker. The calculator accepts any valid calendar date.
- Set as-of date (optional) — Leave blank for today, or choose a specific date to see age on that day — useful for eligibility or historical records.
- Read the breakdown — See years, months, days, and total days lived. For date math between two events, try the date calculator.
Common use cases
- Enter birth date: Pick the date of birth using the date picker.
- Set as-of date (optional): Leave blank for today, or choose a specific date to see age on that day — useful for eligibility or historical records.
- Read the breakdown: See years, months, days, and total days lived.
- Bookmark for quick access: Save the tool for repeat tasks without installing an app.
Frequently asked questions
How is age in years, months, and days computed?
The tool subtracts the birth date from the as-of date, counting full years first, then remaining months, then days — respecting varying month lengths and leap years.
Can I calculate age as of a past date?
Yes. Set the as-of date to any day on or after the birth date to see exact age on that specific day.
What is total days lived?
Total days is the exact count of calendar days between birth and the as-of date, including leap days.
Can I use this for age eligibility checks?
Yes. Set the as-of date to the eligibility deadline and confirm whether the person meets the required age in years or months.
Is this age calculator free?
Yes. Unlimited calculations with no signup; dates never leave your browser.
