Age Calculator
Your exact age in years, months and days, with total days lived and your next birthday.
31years old
Your age
31 years, 4 months, 1 days
Time lived
Total days lived11,446
Total months376
Next birthday 15/06/2027 — 242 days
On the lunar calendar
Traditional age32
The traditional East Asian count starts at one at birth and advances at Lunar New Year, so it runs one to two years ahead.
How it works
An exact age is not a day count divided by 365. It is whole years, then whole months, then leftover days, measured against the real length of each month.
Borrowing is where this usually goes wrong. Many tools subtract the day, month and year fields and borrow 30 days when the day comes out negative. From 31 January to 1 March in a non-leap year, borrowing February’s 28 days lands on minus two. This page instead walks to the most recent monthly anniversary that has actually passed and counts leftover days from there, which gives the 1 month 1 day a person would say.
Alongside the Gregorian age it reports the lunar birth date, the sexagenary year and the zodiac animal. The lunar conversion uses the Vietnamese algorithm at UTC+7, so it matches Vietnamese perpetual calendars rather than the Chinese one.
Tuổi mụ, the traditional count, is not "Gregorian age plus one". A newborn is already one, and everyone gains a year at Tết rather than on their birthday. The gap against the Gregorian age is therefore one or two, depending on where the birthday sits relative to Tết and to today.
The birthday countdown uses the Gregorian calendar. If you mark your birthday by the lunar date, take the lunar date shown in the result and convert it forward for the year you want, since the same lunar date lands on different Gregorian dates each year.
Formula
age = whole months elapsed ÷ 12 (quotient in years, remainder in months) + days since the most recent monthly anniversary • tuổi mụ = current year − lunar birth year + 1
Counting from real monthly anniversaries rather than borrowing a fixed 30 days is what makes end-of-month birthdays come out right.
Worked example
Born 31 January, measured on 1 March of a non-leap year:
- Most recent monthly anniversary
- 28 February
- Whole months
- 1 month
- Days since that anniversary
- 1 day
- Result
- 1 month 1 day
- Field subtraction borrowing 28 days
- −2 days (wrong)
Birthdays on the 29th, 30th and 31st are where age calculations diverge. That is why this walks real anniversaries instead of doing arithmetic on three separate date fields.
Frequently asked questions
How does tuổi mụ differ from an ordinary age?
A newborn counts as one, and everyone gains a year at Lunar New Year rather than on their birthday. So it runs one or two years ahead of the Gregorian age depending on the time of year — not a fixed offset.
Why is my zodiac animal not the one for my birth year?
Zodiac animals follow the lunar year. Anyone born between 1 January and the day before Tết still belongs to the previous lunar year’s animal.
How are end-of-month birthdays handled?
By stepping to the last monthly anniversary that has genuinely passed and counting from there. For someone born on the 31st, February’s anniversary is the last day of February — matching how a person would count it.
Does the total day count include leap days?
Yes. Total days are counted directly between the two dates, so every 29 February you have lived through is included; no 365.25-day approximation is used.
When is my lunar birthday this year?
The result shows the lunar date you were born on. Convert that date forward for the year you want with the lunar calendar tool — the same lunar date can move by up to a month between years.
Which age do official processes use?
Vietnamese administrative processes use the Gregorian age from the birth certificate. Tuổi mụ belongs to cultural use: matching ages for marriage, choosing a year to build a house, celebrating longevity.
Why is a future birth date rejected?
Because there is no sensible reading of a negative age. It returns a warning rather than a meaningless number — usually the year was mistyped.