Baby Milestone Tracker
Track your baby's developmental milestones. See expected ages for common milestones.
About this calculator
This calculator's core job is simple arithmetic: it takes a birth date and reports how old your baby is right now in three units -- days, weeks, and months -- so you always have an exact figure to compare against a pediatrician's growth chart or milestone checklist. Because the "current" side of the calculation is today's date, results update automatically every time you revisit the page rather than needing to be recalculated by hand. Birth Date is naturally the only input, and for any realistic birth date, moving it later (a more recent birth date) reduces every age output, since a more recent birth means less elapsed time; moving it earlier increases them.
Age in Months uses an average days-per-month conversion (about 30.44 days) rather than counting actual calendar months, since calendar months vary in length -- for precise same-day-of-month tracking (for example, "she turns 6 months old on the 14th"), calculating from the calendar date directly will be more exact than this averaged figure. Developmental milestones themselves vary widely between individual babies, and typical ranges span months rather than days -- treat this calculator as a precise age tracker to pair with your pediatrician's own milestone checklist and well-child visit schedule, not as a source of specific expected milestone timing on its own.
Inputs
Results
Age in Days
90
How to Use This Calculator
- Enter your baby's birth date as a timestamp in the Birth Date field (the default is preset to 90 days ago) to calculate their current age automatically.
- Review the age in days, weeks, and months displayed at the top.
- Browse the milestone table to see the expected age (in weeks) for common developmental milestones.
- Check the Reached column to see which milestones your baby's current age has already passed -- this is a read-only reference, not an interactive checklist.
- Share the milestone summary with your pediatrician at well-child visits.
How the result changes with Birth Date
| Birth Date | Age in Days |
|---|---|
| 891,516,952,250 | 10,408 |
| 1,337,275,428,375 | 5,249 |
| 1,790,809,904,499 | 0 |
What each input means
- Birth Date
- Baby's birth date (timestamp).
How this is calculated
Worked example, using the default values
- Identify Input ParametersBirth Date = 1783033904500 = 1 input(s) provided
- Calculate Age in DaysAge in Days90 = 90
- Calculate Age in WeeksAge in Weeks12 = 12
- Calculate Age in MonthsAge in Months2 = 2
Engine last updated . Checked against 2 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
Why does Age in Months show a decimal instead of a whole number?
Because it's calculated using an average month length (about 30.44 days, based on the 365.25-day average year divided by 12) applied to the exact number of elapsed days, rather than counting whole calendar months. That average-based approach means the figure won't always land on a clean whole number the way "the baby turned 3 months old yesterday" would if you counted by calendar date instead.
Why do the age figures update every time I open the page?
The calculation always compares your entered birth date against today's actual date at the moment you load the page, so age in days, weeks, and months increases by itself over time without you needing to re-enter anything. This is different from a calculator with two fixed dates you supply yourself -- here, one side of the comparison is always "right now."
Is this calculator a substitute for a pediatrician's milestone checklist?
No -- it computes precise chronological age only. Actual developmental milestones (smiling, rolling over, sitting up, crawling, first words, walking) vary widely between individual babies and are typically described by pediatricians as broad ranges spanning multiple months rather than a single expected week or day. Use this calculator's exact age figures alongside your pediatrician's own milestone checklist and well-child visit schedule for developmental guidance.
Does entering a future birth date work?
The input is capped at today's date as its maximum, since a birth date in the future doesn't correspond to a baby who has actually been born yet. If you're tracking a pregnancy rather than a born baby's age, a due-date calculator is the more appropriate tool -- this one is designed to measure elapsed time since an actual birth date.
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