Two ceremonies, two milestones
Đầy tháng marks one month, thôi nôi marks one year. They are easy to mix up, and Vietnamese relatives notice immediately when a card has it wrong.
Đầy tháng — the first full month
Held when the baby turns one month old. The family lays out an offering to thank the Twelve Midwives, the Bà Mụ, and Đức Ông, the spirits believed to have shaped the child, and then shares the good news with relatives. For many families it is also when the baby’s name is first announced in front of everyone.
Thôi nôi — the first year
Thôi nôi literally means "leaving the cradle", and it falls on the baby’s first birthday. There is another offering to the Bà Mụ, and the part everyone waits for: a few objects — a pen, a comb, a coin — are laid in front of the child, and whichever one they reach for is taken as a playful hint about the life ahead.
The date comes from the lunar calendar
Both ceremonies are normally counted from the lunar birth date, not the ordinary one. Many families follow the saying gái lùi hai, trai lùi một — hold it two days earlier for a girl, one day earlier for a boy — and the exact custom varies by region and by family.
Who gets invited
Unlike a wedding, a baby’s celebration is usually small: grandparents, aunts and uncles, a few close friends of the parents. Because it is small, knowing the numbers in advance matters more — one table too many or too few is obvious.