Age Calculator
Choose a mode and enter your dates
Results
Age calculation results in your preferred format
How it works:
The calculator automatically handles leap years and month-length variations. For February 29 birthdays, it uses February 28 in non-leap years.
How It Works
Select calculation mode, enter dates, and get instant results. Our calculator uses precise date arithmetic accounting for leap years and month variations.
Common Uses
Calculate exact age for legal purposes, track child development milestones, determine service length, or find intervals between historical events.
Always Accessible
Works completely in your browser - no data sent to servers. Use it anytime, anywhere with full privacy protection.
How the Age Calculator Works
- Select calculation mode: "Calculate Age" for age from birth, or "Date Interval" for time between any two dates
- Enter your dates - the calculator validates they're logical (start date ≤ end date)
- The system calculates total days between dates using precise date arithmetic
- For age in years/months/days, it adjusts for month lengths and leap years intelligently
- When converting to years, it accounts for whether the end date's day has passed the start date's day
- Leap years are automatically factored in (every 4 years, except century years not divisible by 400)
- Results update instantly as you change dates or calculation mode
- Choose your preferred output format from the unit selector buttons
Age Calculation Logic
The calculator uses precise date arithmetic rather than approximations:
- Total Days Calculation: Direct date subtraction using JavaScript Date objects, converted to milliseconds and then to days
- Leap Year Handling: The year is a leap year if divisible by 4, except if divisible by 100 but not by 400 (e.g., 2000 was leap year, 1900 was not)
- Month-End Logic: For calculations like "January 31 to February 28," the system correctly treats February 28 as the month-end equivalent
- Variable Definitions: StartDate (initial date), EndDate (final date), TotalDays (difference in days), YearDiff (year component), MonthDiff (month component), DayDiff (day component)
Step-by-Step Examples
Child's Age for School Enrollment
Leap Year Calculation
Service Length Calculation
Use Cases
Age calculations are essential for various personal, professional, and historical purposes. Understanding exact ages and date intervals helps with planning, verification, and accurate record-keeping.
Legal Age Verification
Precisely determine if someone meets age requirements for driving licenses (typically 16-18 years depending on location), retirement benefits (often 65+ years), voting eligibility (18+ years in most countries), or age-restricted activities. School enrollment often requires children to be a specific age by a cutoff date - this calculator provides the exact verification needed.
Child Development Tracking
Parents and pediatricians can track exact age milestones for growth charts and developmental assessments. Medical professionals use precise age calculations for vaccine schedules, medication dosages (often weight and age-based), and developmental milestone tracking. Even a few days' difference can matter in early childhood development.
Practical Example: School Enrollment
Scenario: A child was born on August 15, 2018. The school cutoff date is September 1, 2023.
Calculation: Using our calculator, you'll find the child is exactly 4 years, 1 month, and 17 days old on September 1, 2023.
Decision: If the school requires children to be 5 years old by September 1, this child would need to wait another year, as they won't turn 5 until August 15, 2024.
Employment & Service Length
Calculate exact tenure for employment benefits, pension calculations, or service awards. Human resources departments use precise date calculations for determining eligibility for benefits, calculating accrued vacation time, and anniversary recognitions. Even one day can make a difference in benefit eligibility in many organizations.
Event Planning
Determine exact time until birthdays, anniversaries, project deadlines, or special events. Event planners use date calculations for countdowns, scheduling, and milestone celebrations. Knowing exactly how many days remain helps with venue bookings, invitation timing, and preparation schedules.
Historical Research
Calculate precise intervals between historical events, artifact ages, or generational timelines. Historians and genealogists rely on accurate date calculations for timelines, age determinations of historical figures at key events, and understanding temporal relationships between historical occurrences.
How to Read the Results
Years/Months/Days Format
This shows the complete age breakdown. "5 years, 2 months, 15 days" means exactly that duration has passed. For planning purposes, note that months vary in length (28-31 days). This format is most useful for human-readable age reporting and legal documentation where precise age matters.
Total Days
The absolute count of days between dates, useful for scientific calculations, contractual periods, or when precise daily counting matters. This format eliminates month-length variations and provides a single, unambiguous number. Use this for calculations where you need to multiply by daily rates or count exact durations.
Weeks/Months View
Alternative perspectives that might be more relevant for project timelines, pregnancy tracking (often measured in weeks), or monthly billing cycles. The weeks view divides total days by 7, showing full weeks and remaining days. The months view shows total months (calculated from years × 12 + months) plus remaining days.
Next Birthday Calculation
Helps with planning celebrations or age-related transitions by showing exactly when the next age milestone occurs. For February 29 birthdays, the calculator correctly shows February 28 in non-leap years, following standard legal practice. This feature is particularly useful for planning events, sending reminders, or tracking age-based eligibility changes.