Know exactly where you stand in time.
From your age in years, months, and days — to biological age, heart age, retirement milestones, and even how old you'd be on Mars. Instant, free, private.
Every age question, answered.
Six categories, 30+ free calculators. Pick a category to filter, or browse everything below.
Calculate your exact age in years, months, days, and hours from your date of birth.
Find the exact age gap between two people down to years, months, and days.
Measure the relationship age gap and understand what it means in life-stage terms.
Days until your next birthday, day of the week you were born, and your zodiac sign.
Calculate the duration between any two dates — in years, months, days, and business days.
The precise Y:M:D borrowing-method age calculation used in professional assessments.
Age formatted for Pearson clinical assessments, with step-by-step borrow audit trail and printable report.
Corrected age for premature infants — chronological age minus weeks born early, per AAP guidance.
Estimate your biological age from lifestyle factors — activity, sleep, BMI, smoking — based on published cohort research.
Compare your cardiovascular age to your chronological age using a Framingham-derived risk estimate.
A lighthearted quiz about your mindset and reactions — for entertainment only, not clinical assessment.
Estimate your fitness age from resting heart rate and activity level using VO2max-based norms.
Calculate your estimated due date using Naegele's Rule from your last menstrual period.
Find how many weeks and days pregnant you are from your last menstrual period.
Track your baby's age in weeks and months with milestone reference points.
Find your Full Retirement Age by birth year and see early vs. delayed claiming impacts.
See where your net worth ranks compared to Federal Reserve survey data for your age group.
Calculate total work tenure in years, months, and days for pension or benefit eligibility.
Convert your dog's age to human years using the UC San Diego epigenetic formula — not the outdated ×7 myth.
Find out how old you'd be on every planet in the solar system based on their orbital periods.
Estimate a tree's age from its trunk circumference and species using the growth-factor method.
Numbers that change real decisions.
Age isn't just a birthday — it's a threshold. The right number at the right time can affect your legal rights, health planning, and financial future.
For Real Decisions
Retirement eligibility, Social Security claiming age, Required Minimum Distributions, and legal age thresholds all depend on exact birth-year calculations. Our tools use the same methods professionals use.
For Curiosity
How old is your dog in human years, really? How old would you be on Saturn? What does your resting heart rate say about your fitness age? Not every calculation changes a decision — some just expand how you see yourself in time.
For Planning Ahead
School enrollment cutoffs, pregnancy milestones, developmental age assessments, and pension tenure calculations all benefit from knowing the precise number — not an approximation.
Why "just divide by 365" is wrong
A year isn't 365 days long — it's 365.2422 days, accounting for leap years. Over a lifetime, this adds up. Someone who is 40 years old today has lived through 9 or 10 leap years depending on their exact birthday. That's 9–10 extra days that a simple ÷365 calculation throws away.
The right way to calculate age is the Y:M:D borrowing method: subtract days, then months, then years — borrowing from the next unit up whenever a component goes negative, using the actual number of days in each calendar month. This is what professional clinical tools use, and it's what every Chronly calculator uses.
Step 1: Days
Subtract the birth day from the reference day. If the result is negative, "borrow" from the months — adding the actual number of days in the previous month of the reference date.
Step 2: Months
Subtract the birth month from the reference month. If the result is negative after borrowing, subtract 1 from years and add 12 to months. This handles the December-to-January crossover correctly.
Step 3: Years
Subtract the birth year from the reference year. After the borrowing adjustments above, this gives the completed full years, with no rounding and no leap-year error.
Why It Matters
For clinical assessments (developmental, Pearson, Brigance), being off by even one day can put a child in the wrong age band. For retirement calculators, the exact birth year determines your Full Retirement Age to within a single month.