Baby Age Calculator — Exact Age in Days, Weeks and Months
Enter your baby's date of birth and today's date to instantly see their exact age in days, weeks, months and years — all at once.
Baby's date of birth
Today's date
1y 5m
How does this calculator work?
Subtract date of birth from today to get total days, divide by 7 for weeks, and count whole calendar months for age in months. This calculator shows all four units — days, weeks, months and years — so parents and clinicians can read whichever unit their growth chart, vaccination schedule or milestone guide requires.
Formula
How this is calculated
The calculator subtracts the date of birth from today to find the total elapsed whole days. Weeks are found by dividing total days by 7; the remainder gives the extra days. Calendar months are counted by year/month arithmetic with a day-of-month correction — a baby born on the 15th of a month is exactly 1 calendar month old on the 15th of the following month, not on the 14th or 16th. Calendar years are floor(calendar months ÷ 12).
For babies under 12 weeks, paediatricians and neonatal units track age in completed weeks; from around 3 months onward, months become the standard unit. Growth charts, vaccination schedules and developmental milestone guides are keyed to month-based age, so showing all four units simultaneously lets parents and clinicians pick whichever suits. The day count is most critical in the first two weeks for monitoring birth-weight recovery.
All dates are handled as local midnight so there are no time-zone artefacts. A date of birth in the future gives no result — use the Due Date Calculator for estimating a future birth date. For premature babies, the corrected (adjusted) age — counted from the original due date, not the birth date — is the appropriate comparison for developmental milestones.
Frequently asked questions
Clinical teams track premature and newborn babies in completed weeks until around 12–16 weeks, then switch to months. Vaccination cards and WHO growth charts use months. For premature babies, use the corrected age (weeks from due date) for developmental comparisons.
A premature baby's corrected age is calculated from their original due date. If a baby arrived 8 weeks early and is now 6 months old by birth date, their corrected age is 4 months — use this for growth-chart and milestone comparisons until at least 2 years of age.
Calendar months have different lengths (28–31 days), so counting whole calendar months is not the same as dividing total days by 30.4. The calendar method is the standard medical convention and can differ from the day-division estimate by one near transition points.
TG we-Calculate Editorial Team. (2026). Baby Age Calculator — Exact Age in Days, Weeks and Months [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/baby-age-calculator
TG we-Calculate Editorial Team. "Baby Age Calculator — Exact Age in Days, Weeks and Months." TG we-Calculate. 2026. https://we-calculate.com/calculator/baby-age-calculator.
TG we-Calculate Editorial Team, "Baby Age Calculator — Exact Age in Days, Weeks and Months," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/baby-age-calculator
@misc{wecalculate_baby_age_calculator, title = {Baby Age Calculator — Exact Age in Days, Weeks and Months}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/baby-age-calculator}}, year = {2026}, note = {TG we-Calculate} }
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