Baby Age Calculator
Find your baby’s exact age in days, weeks and months — the way paediatricians and milestones use it.
Formula last reviewed 4 August 2026 · How we verify our calculators
Baby’s age
31 months
- In weeks
- 135
- In months
- 31
- In days
- 946
Updates live as you type
Frequently asked questions
For newborns, weeks give a more meaningful picture of rapid early development, which is why paediatricians and milestone guides use weeks before switching to months.
Commonly around two months (about 8–9 weeks). This calculator shows weeks under 60 days and months thereafter, matching that convention.
They are calendar months between the birth date and today, so the figure lines up with how check-ups and vaccination schedules are described.
It helps you see your baby’s current age at a glance, but always follow the official immunisation schedule and your paediatrician’s advice for exact dates.
"4 weeks" today, "3 months" two months from now — same baby, different unit
A baby born on 1 January 2024, checked at 1 February 2024 — 31 days later — gets reported here as "4 weeks", because this calculator switches its display convention at the 60-day mark. Check the same baby again at 1 April 2024 — 91 days in, 3 full calendar months — and the label changes to "3 months" instead of counting further weeks. Nothing about the underlying calculation changed; only which unit makes the number meaningful did.
Why paediatric convention switches units around two months
Weeks give a far more useful picture of a newborn's first couple of months, when development moves fast enough that a monthly figure would blur real changes together. Once a baby passes roughly the two-month mark, growth settles into a pace better tracked against monthly check-ups, and months become the more natural unit — which is exactly why paediatricians and milestone charts make the same switch this calculator does. The date math itself stays calendar-exact throughout, correctly accounting for different month lengths rather than assuming a flat 30-day month.
What this number is actually useful for
Beyond simply satisfying curiosity, a precise age readout helps line up developmental milestones against what's expected at a given week or month, and keeps a clear reference point between paediatrician visits. One place to be careful: for vaccination timing specifically, always follow the official immunisation schedule and your paediatrician's guidance directly rather than working backward from a rounded age figure here — immunisation windows are specified precisely enough that "about 8 weeks" isn't a substitute for the exact scheduled date.
This is an estimate based on standard assumptions, not medical advice. Pregnancy dating and growth can vary — consult your doctor for personalised assessment, especially if cycles are irregular.