What is Vietnamese lunar age?
Lunar age equals the current year minus the birth year, plus one. Someone born in 1990 is 37 in 2026, even before their Gregorian birthday. It is the number folk calculations use.
Also called: East Asian age reckoning
What is tuổi mụ?
Tuổi mụ, also called tuổi âm or tuổi ta, is the traditional way Vietnamese people and several East Asian countries count age. The formula is simple: take the current year, subtract the year of birth, then add one.
Someone born in 1990 is 37 in tuổi mụ in 2026, while their Western age may only be 35 or 36 depending on whether their birthday has passed.
Why does tuổi mụ add one?
This way of counting comes from the belief that time in the mother's womb is also part of a person's life: a child is counted as one year old at birth. From there, age increases at the start of the new year rather than on a birthday, so everyone born in the same year shares the same tuổi mụ for the whole year.
Where is tuổi mụ used?
Tuổi mụ is the number most folk calculations use, not Western age:
- Kim Lâu: take tuổi mụ, divide by 9, and look at the remainder.
- Hoang Ốc: count the six palaces according to tuổi mụ.
- Ruling star (Cửu Diệu): look up the star by tuổi mụ and gender.
- Many other customs, such as longevity celebrations and checking ages for marriage.
This is why mixing up tuổi mụ and Western age is the most common mistake people make when checking their own fortunes: being off by one year can flip a result entirely from not violating a taboo to violating it.
One point to note about tuổi mụ
There is a stricter method that adjusts for the timing of Tết Nguyên Đán (the Lunar New Year) so that people born before and after the holiday are not lumped together. However, the folk lookup tables in circulation all use the simple subtraction above, so when comparing results between sources, make sure both sides are using the same convention.
How does tuổi mụ compare with full age, calculated for 2026?
| Year of birth | Year checked | Full age (approximate) | Tuổi mụ |
|---|---|---|---|
| 1990 | 2026 | 36 | 37 |
| 1995 | 2026 | 31 | 32 |
| 2000 | 2026 | 26 | 27 |
| 2005 | 2026 | 21 | 22 |
| 2010 | 2026 | 16 | 17 |
Tuổi mụ is always exactly one more than full age, because the old way of counting treats time in the mother's womb as one year of life. Every lookup for Kim Lâu, Hoang Ốc and Tam Tai uses tuổi mụ, and using full age by mistake throws the entire result off by one step.
The figures in the table match the results from the lookup tools on Nhật Nguyệt.
