Lunar Calendar Converter

How solar-lunar date conversion works

This page runs a Ho Ngoc Duc-derived new-moon and solar-term algorithm with a UTC+8 day boundary. It is an algorithmic reference mode, not a verified official calendar for a particular country.

The published validation set—31 Vietnamese Tết dates from 1996–2026, 100 round trips and the lunar engine tests—covers only the UTC+7 Vietnamese mode. We do not claim that validation for this UTC+8 output.

How do I convert a date between the solar and lunar calendar?

This page runs a Ho Ngoc Duc-derived new-moon and solar-term algorithm with a UTC+8 day boundary. It is an algorithmic reference mode, not a verified official calendar for a particular country.

Steps to convert a date

1. Choose Solar to Lunar or Lunar to Solar with the toggle at the top of the tool.
2. For Solar to Lunar, pick any date between 1900 and 2100 using the date picker.
3. For Lunar to Solar, enter the lunar day, month, and year, and check the leap-month box only if you specifically mean the intercalary (leap) version of that month.
4. Read the converted date, plus the zodiac animal year shown alongside it.
5. If Lunar to Solar shows an error, the day/month/leap combination you entered does not exist in that lunar year — double check whether the month you mean was actually a leap month that year.

How the lunar month and leap month are determined

• New moon = the moment the moon is between Earth and the sun, computed to sub-day precision using a periodic astronomical formula
• Leap month (nhuận) = an inserted 13th lunar month in certain years to keep the lunar calendar aligned with the solar year over time; the specific month that repeats varies by year
• UTC+8 — This page runs a Ho Ngoc Duc-derived new-moon and solar-term algorithm with a UTC+8 day boundary. It is an algorithmic reference mode, not a verified official calendar for a particular country.

[UTC+7 Vietnamese validation example] Common lunar-to-solar date lookups

[UTC+7 Vietnamese validation example] When is Tet (lunar new year) in 2026?

[UTC+7 Vietnamese validation example] Lunar 1/1/2026 falls on solar February 17, 2026, calculated the same way this tool converts any Lunar to Solar date.

[UTC+7 Vietnamese validation example] When is the mid-autumn festival in 2026?

[UTC+7 Vietnamese validation example] Lunar 15/8/2026 falls on solar September 25, 2026.

[UTC+7 Vietnamese validation example] When is Tet (lunar new year) in 2027?

[UTC+7 Vietnamese validation example] Lunar 1/1/2027 falls on solar February 6, 2027.

[UTC+7 Vietnamese validation example] When is Tet (lunar new year) in 2025?

[UTC+7 Vietnamese validation example] Lunar 1/1/2025 falls on solar January 29, 2025 (Year of the Snake), as also shown in the example table above.

[UTC+7 Vietnamese validation example] When is Tet (lunar new year) in 2024?

[UTC+7 Vietnamese validation example] Lunar 1/1/2024 falls on solar February 10, 2024 (Year of the Dragon), as also shown in the example table above.

[UTC+7 Vietnamese validation example] Which lunar month is the leap month in 2025?

[UTC+7 Vietnamese validation example] Lunar year 2025 has an intercalary leap 6th month (nhuận tháng 6), inserted because that lunar year contains 13 new moons between two winter solstices.

[UTC+7 Vietnamese validation example] Example date conversions

Frequently asked questions

Which time-zone mode does this page use?

This page runs a Ho Ngoc Duc-derived new-moon and solar-term algorithm with a UTC+8 day boundary. It is an algorithmic reference mode, not a verified official calendar for a particular country. A date near a new-moon boundary can change with the UTC offset; check important traditional or legal dates against the relevant authoritative almanac.

What is a leap month, and why do some years have one?

The lunar calendar's 12 months (each starting at a new moon) add up to about 354 days, roughly 11 days short of the 365-day solar year, so every two to three years an extra 13th month is inserted to keep lunar New Year from drifting far from late winter; the leap month takes the number of the preceding regular month, so a leap month 4 comes right after month 4.

Why do I need to specify whether a lunar month is a leap month when converting Lunar to Solar?

In a year with a leap month, two different periods of the solar calendar share the same lunar month number, so entering just a day and month is ambiguous; checking the leap-month box tells the converter which of the two you mean.

How accurate is this for very old or far-future dates?

The published validation set—31 Vietnamese Tết dates from 1996–2026, 100 round trips and the lunar engine tests—covers only the UTC+7 Vietnamese mode. We do not claim that validation for this UTC+8 output.

The published validation set—31 Vietnamese Tết dates from 1996–2026, 100 round trips and the lunar engine tests—covers only the UTC+7 Vietnamese mode. We do not claim that validation for this UTC+8 output. A date near a new-moon boundary can change with the UTC offset; check important traditional or legal dates against the relevant authoritative almanac.

Privacy and safety

• Runs in your browser — Everything you type is calculated on your own device. Your inputs are never sent to a utilduck server.
• Encrypted connection — Pages are served over HTTPS, so nobody on the network can read what you load.
• Not shared with third parties — Your inputs are not passed to analytics or advertising services.
• Nothing is stored — Results are not saved to any server, and there is no account to create.

Last updated: 2026-08-24