Baby Milestone Dates

Features

• Lists both “100 days after birth” and “the hundredth day”, without choosing a convention for you
• One month and one year use “same day next month”, so a 31 January birth does not land on 3 March
• Each milestone shows “in N days”, “N days ago” or “today”
• Age is computed as real calendar years, months and days — not days divided by 30
• A 29 February birth gets an explicit note about common years
• “Count from” lets you look back at a past date or plan ahead
• Optionally hide milestones that have already passed
• Computed locally; the date never leaves the page

How to use

1. Enter the date of birth (2026-03-05 or 2026/3/5 both work)
2. The milestones and countdowns appear immediately
3. Change “Count from” to look at a different day
4. Tick the checkbox to keep only upcoming milestones

FAQ

Is the hundredth day 99 days after birth or 100?

Both conventions are in use, so this tool lists both: counting the birth day as day 1 makes the hundredth day the 99th day after birth, and counting it as day 0 makes it the 100th. The table has a row for each, with its own date. Local custom varies, and rather than pick one and be wrong for half its users, it states both.

Why is one month not 30 days?

Because “one month old” means the same day of the next month, not a fixed span. Counting 30 days would put a baby born on 31 January at one month on 2 March, when in fact they turn a month on 28 February. This uses “add a month, clamp to the end of that month if the day does not exist”, so 31 January → 28 February and 31 May → 30 June. Adding a month to a JS `Date` does not do this: it overflows rather than clamping, turning 31 January into 3 March.

When is the birthday for someone born on 29 February?

This tool takes the birthday in common years as 28 February and says so explicitly in the result. Conventions differ — 28 February and 1 March are both used. Rather than quietly choosing, it shows which one it used. The “months and days” part of the age line follows the same rule.

Why is there no traditional Chinese nominal age?

Because it is counted from the lunar calendar: a baby is 1 at birth and gains a year at each lunar new year. This tool has no lunar data, and faking it from the Gregorian date would be off by a year in places — worse than leaving it out. (Lunar conversion is a separate job that needs a lunar dataset to do correctly.)