How to Calculate Age from Date of Birth
Quick Answer
Your age = Current date - Birth date. Use an age calculator to get your exact age in years, months, and days instantly. Manual calculation requires subtracting birth year from current year, then adjusting for whether your birthday has passed.
When You Need to Calculate Age
Calculating exact age comes up in many situations:
- Eligibility verification — Age requirements for services, programs, or benefits
- Medical records — Accurate age for healthcare decisions
- Legal documents — Contracts, consent forms, and legal proceedings
- Insurance — Premium calculations and coverage eligibility
- Personal curiosity — Finding your exact age in years, months, and days
Step-by-Step: Calculate Age
Go to the age calculator and enter the birth date. Use the date picker or type the date manually.
By default, age is calculated as of today. You can set a different target date to find age on a specific date (past or future).
The calculator shows age in years, months, and days, plus total days and weeks since birth.
How Age Calculation Works
Age is more than just subtracting birth year from current year:
Years
Count how many complete years have passed since birth. A person born in 1990 is not 35 years old until their birthday in 2025 has passed.
Months
After counting complete years, count the remaining complete months since the last birthday.
Days
Finally, count the remaining days after the last complete month.
Birth date: March 15, 1990
Today: July 8, 2025
Age: 35 years, 3 months, 23 days
Common Use Cases
Eligibility Checks
A program requires participants to be at least 18 years old. Enter the birth date to verify if someone meets the age requirement as of today or a specific date.
Medical and Healthcare
Healthcare providers need exact age for dosing, screening recommendations, and treatment protocols. Pediatric care especially requires precise age in months.
Retirement Planning
Calculate how many years until retirement age (e.g., 65) or determine if someone has reached retirement eligibility.
School Enrollment
Schools have cutoff dates for age eligibility. Calculate a child's age as of the enrollment cutoff date to determine grade placement.
Insurance and Benefits
Life insurance premiums, social security eligibility, and senior discounts all depend on exact age calculations.
Age on a Specific Date
Sometimes you need to know how old someone was or will be on a particular date:
- Historical research — How old was a historical figure when an event occurred?
- Legal cases — Age at the time of an incident
- Future planning — How old will you be on a milestone date?
- Document verification — Was someone of legal age when they signed?
Legal age matters: For legal purposes, age is typically calculated as of the specific date in question, not rounded. Someone born on July 15 is not 18 on July 14.
Age in Different Units
Age can be expressed in various ways:
- Years, months, days — Most common and precise format
- Total days — Useful for calculations and comparisons
- Total weeks — Common for infant age
- Decimal years — Used in scientific and statistical contexts
Common Mistakes to Avoid
- Simple year subtraction — Doesn't account for whether the birthday has occurred this year
- Ignoring leap years — Can affect precise day counts
- Wrong date format — Confusing MM/DD/YYYY with DD/MM/YYYY leads to errors
- Time zone issues — Birth time zones can matter for exact calculations
- Rounding errors — Age should not be rounded up before the birthday
Related Calculations
Once you have age, you might also need:
- Days until next birthday — Plan celebrations in advance
- Date duration — Calculate days between any two dates using our date duration calculator
- Zodiac sign — Often determined by birth date