How to Calculate Age from Date of Birth Online
Whether you're filling in a form, planning a milestone birthday, or verifying someone's age for a document, knowing your exact age in years, months, and days matters. This guide shows you how to calculate it in seconds using a free online tool.
How Age Is Calculated
Age calculation is more complex than simple subtraction because months have different lengths and leap years add an extra day every four years. The correct approach is:
- Start with complete years elapsed since birth date
- Add remaining complete months after the last birthday
- Add remaining days after the last complete month
For example: born 15 March 1990, calculating on 20 July 2025 → 35 years, 4 months, 5 days.
Step-by-Step Instructions
Open the Age Calculator
Navigate to the free Age Calculator. It runs entirely in your browser — no account or app needed.
Enter your date of birth
Click the date input and select your birth date. You can type the date directly (YYYY-MM-DD) or use the date picker.
Set the "as of" date
This defaults to today. Change it to calculate age at a specific past or future date — useful for checking age eligibility at a particular date.
View your exact age
The result shows your age as years, months, and days. It also displays the total days you have been alive — useful for milestone celebrations.
Check your next birthday
The calculator also shows how many days remain until your next birthday, so you can plan ahead.
Common Use Cases
- Filling in forms: Know your precise age in years and months for medical or legal paperwork
- Age verification: Check if someone meets an age threshold (18+, 65+) on a specific date
- Birthday planning: Find out how many days until a milestone birthday
- Health records: Calculate a patient's or child's age at a past appointment date
Calculate your exact age now
Years, months, days, and next birthday countdown — 100% browser-based, no uploads, no account.
Open Age Calculator