Your Baby’s First-Year Milestones: 50, 100, 200 and 365 Days

Why days, not months

Months vary in length, so “three months old” is a range, not a date. Day counts are exact: 100 days after a birth date is one specific date, and it is the same calculation whether the span crosses February or a leap day. That precision is why traditions like the baek-il and the 100-day celebration use day counts rather than month counts.

Days also make comparison easy: two babies born a month apart reach their 100-day dates a month apart, and the gap between any two milestones is a fixed number of days, not a variable number of months.

The first-year ladder

50 days (20 February 2026 for a 1 January birth) is the early milestone: the baby is usually smiling socially and settling into a routine. 100 days (11 April 2026) is the baek-il in Korea and a common celebration date elsewhere — rice cakes, family, photographs. 200 days (20 July 2026) is roughly six and a half months — often the start of weaning and sitting. 365 days (1 January 2027) is the first birthday, the dol in Korea and the milestone every family marks, with the doljabi ritual in Korean tradition.

The ladder is a planning tool as much as a celebration list: each date is a natural point to take the photograph, make the appointment or send the update that the family will want later.

The traditions behind the numbers

The 100-day celebration is the most tradition-rich of the four: Korea’s baek-il with Samsin offerings and rice cakes shared with 100 people, China’s bai ri yan and Vietnam’s le thoi noi. The first birthday carries its own traditions everywhere — Korea’s dol and doljabi, where the baby chooses among objects said to predict its future, and the smash-cake and first-birthday party familiar across the English-speaking world.

The 50- and 200-day marks have no single tradition, which is their advantage: they are yours to define. Families use them for the photograph series, the health-visitor check or simply the message to grandparents that the baby has reached another stage.

The weekday matters

Milestone dates fall on arbitrary weekdays — 11 April 2026 is a Saturday, but the next baby’s 100-day date might be a Tuesday. That is why the calculator gives the weekday alongside the date: celebrations are planned for weekends, and the exact date and the celebration date are often different by design.

Counting conventions: the one-day trap

This site counts the birth day as day zero and adds the day count. Inclusive counting — birth day as day one — gives a date one day earlier, and it is the traditional Korean way of counting both ages and the baek-il. Neither is wrong; they are different conventions. When a date matters (an invitation, a record, a medical note), state the convention.

Planning around the ladder

Use the exact dates for the record (the baby book, the photographs, the medical notes) and the nearest weekend for the gathering. Photograph each milestone the same way — same place, same light, same scale object — and the set becomes a visible record of growth that no single photograph can give.

Common mistakes to avoid

Counting the birth day as day one (one day early); substituting “three months” for 100 days; assuming 365 days is always the first birthday (it is, for a non-leap birth year — but a baby born 29 February reaches 365 days on 28 February the following year in common practice, which is a convention worth stating); and forgetting that the weekday is part of the answer.