Your result
How this calculation works
Days are counted between calendar dates, including leap days. Weeks are whole groups of seven days. Monthly milestones are anchored to the birth date; if that day is missing in a month, the last day of that month is used. This is calendar age, not corrected age for premature babies or medical advice.
Find your baby’s calendar age on any selected date, with completed months, weeks and days, and a first-two-years month calendar.
How to use the baby age calculator
- Enter the baby’s birth date.
- Leave the comparison date as today, or select another date.
- Choose Calculate to see the age and all 24 monthly milestones.
How the dates are calculated
Whole days are counted between the two calendar dates. A week is seven days. Each monthly anniversary starts from the original birth date, not from the previous month’s anniversary. If the original day does not exist, that month’s last day is used. For a January 31 birth, the first milestone is February 28 (29 in a leap year) and the second is March 31.
Worked example
For a baby born on June 19, 2021, the age on October 15, 2021 is 3 months and 26 days: 118 days, or 16 weeks and 6 days. The four-month milestone is October 19, 2021.
What this result means
The calendar marks age anniversaries, not developmental deadlines. It does not evaluate growth, medication doses, vaccination timing or corrected age after premature birth. Ask a qualified clinician about individual health or development questions.
Privacy
This calculator add-on processes the dates in your browser without saving them or sending them to a server.
Frequently asked questions
How do I calculate baby age in weeks?
Count the exact calendar days from birth to the comparison date. Divide by seven for completed weeks and keep the remainder as extra days. Months are not assumed to contain four weeks.
What happens for a birth on the 29th, 30th or 31st?
If the birth day does not exist in a target month, use that month’s last day. Each later milestone is calculated again from the original birth date, so dates do not drift.
Can I calculate the age on a future date?
Yes. Set Calculate age on to a future date that is on or after the birth date.
Is this corrected age for a premature baby?
No. It reports calendar age only and does not adjust for gestational age or replace advice from a qualified clinician.