What this calculator does
In the first months, a baby’s age is often described in weeks and later in months. Accurate age tracking helps with appointments, feeding milestones and development checks.
This calculator shows months and extra days, weeks, total days and the next monthly milestone. Premature babies may use corrected age.
Baby age
Months = completed calendar months since birth · Days = remaining days Calendar months account for different month lengths. The next milestone is the birth day in the following month.
How this calculator works
- 01
Enter the birth date
Choose the day, month and year of birth.
- 02
Set a reference date
Today is the default; any other date works.
- 03
Review milestones
See months, weeks, days and the next monthly date.
Frequently asked questions
Is 4 weeks always 1 month?
No. Months have 28–31 days, so four weeks is close to but not exactly one calendar month.
What is corrected age?
For premature babies, corrected age adjusts for weeks born early. Discuss it with your paediatrician.
Which age is used for vaccinations?
Vaccination schedules usually use completed months and days. Follow your national schedule and clinician’s advice.
Data basis: 2026 · Annual constants live in structured JSON files and are updated once a year.
Results are unverified model calculations and do not replace tax, legal or financial advice.