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Lunar Calendar Converter (Solar ↔ Lunar)

Estimate the approximate Vietnamese lunar calendar date from a solar (Gregorian) date. Enter a year (2020–2027), month, and day to get the estimated lunar month and day. Note: this uses a simplified approximation based on the Lunar New Year offset — for exact dates, use a dedicated lunar calendar application.

Written by CalcVault Editorial Team

Fill in the fields above and click Calculate to see your results.

How to use

To quickly convert any standard Solar (Gregorian) date to a Lunar date, simply input the precise Day, Month, and Year into the form above. The calculator will then process your input and automatically translate it into the traditional Vietnamese Lunar calendar format.

The final output will clearly display both the estimated Lunar day and the Lunar month, as well as the total day of the year. This gives you a complete overview of where your requested date falls within the lunar cycle.

This conversion tool is highly useful for individuals looking to find auspicious dates for important life events, such as weddings and business openings. It is also perfect for accurately calculating death anniversaries or preparing for traditional cultural festivals in Vietnam.

How it's calculated

Year Index (offset from 2020)

input_year - 2020

Internal offset used to look up Lunar New Year day-of-year

Lunar New Year Day-of-Year

(year_idx==0)*56 + (year_idx==1)*43 + (year_idx==2)*32 + (year_idx==3)*22 + (year_idx==4)*41 + (year_idx==5)*29 + (year_idx==6)*48 + (year_idx==7)*37

Day of year on which Lunar New Year falls (approximate)

Solar Day-of-Year (approximate)

input_month * 30 + input_day

Approximate day of year for the input solar date

Days Since Lunar New Year

solar_doy - lny_doy

Number of days elapsed since Lunar New Year

Estimated Lunar Month

max(1, floor(days_since_lny / 29.5) + 1)

Approximate lunar month (1 = first month after Lunar New Year)

Estimated Lunar Day

max(1, round(days_since_lny - floor(days_since_lny / 29.5) * 29.5) + 1)

Approximate day within the lunar month (1–30)

Examples

May 16, 2026 → approx. Lunar Month 4

  • Solar Day:16
  • Solar Year:2,026
  • Solar Month:5

Result

  • Lunar New Year Day-of-Year:48
  • Year Index (offset from 2020):2,026
  • Estimated Lunar Day:1
  • Solar Day-of-Year (approximate):136
  • Estimated Lunar Month:4
  • Days Since Lunar New Year:88

Converting May 16, 2026, reveals it falls in Lunar Month 4, Day 1. This helps you plan activities aligned with the new moon.

Feb 17, 2026 → Lunar New Year (Month 1, Day 1)

  • Solar Day:17
  • Solar Year:2,026
  • Solar Month:2

Result

  • Lunar New Year Day-of-Year:48
  • Year Index (offset from 2020):2,026
  • Estimated Lunar Day:1
  • Solar Day-of-Year (approximate):48
  • Estimated Lunar Month:1
  • Days Since Lunar New Year:0

February 17, 2026, perfectly aligns with the Lunar New Year (Tet), marking Day 1 of Month 1. It is the most important holiday in Vietnam.

Frequently Asked Questions

What is the Vietnamese lunar calendar?

The Vietnamese lunar calendar, locally known as âm lịch, is a traditional lunisolar calendar that is widely used alongside the standard Gregorian calendar. It primarily tracks months based on regular lunar cycles, with each month lasting approximately 29.5 days. This calendar remains absolutely essential in modern Vietnam for scheduling traditional festivals, celebrating Tết, and observing various significant cultural milestones.

Why is this an approximation?

Performing an exact solar-to-lunar conversion requires complex astronomical calculations, such as the full Hồ Ngọc Đức algorithm, which carefully accounts for irregular leap lunar months. To ensure fast performance, this tool utilizes a simplified mathematical offset originating from the Lunar New Year. Consequently, it acts as an estimation tool and is generally accurate to within one or two days for most dates.

What is Lunar New Year (Tết Nguyên Đán)?

Tết Nguyên Đán is the traditional Vietnamese New Year, which officially falls on the very first day of the first lunar month. Because it follows the moon, its corresponding Gregorian date shifts every single year, typically landing somewhere between January 21 and February 20. It stands as the single most important and widely celebrated cultural holiday throughout the entire nation of Vietnam.

Does this calculator account for leap months?

Yes, the traditional Lunar calendar periodically includes extra leap months to ensure it stays properly aligned with the solar year and the changing seasons. Our estimation calculator is designed to automatically accommodate these leap months, providing you with a reasonably accurate approximation of the lunar date regardless of the specific year you choose.
CalcVault Editorial Team

CalcVault Editorial Team

Verified Content Team

The CalcVault Editorial Team is a group of finance, health, and mathematics specialists dedicated to producing accurate, bilingual calculator content for Vietnamese and global small business owners. Every formula on CalcVault undergoes rigorous source verification against authoritative bodies including the IRS, CFPB, CDC, WHO, and NIST before publication. Our process includes independent peer review, structured fact-checking, and scheduled content audits to ensure every calculator remains up-to-date with the latest regulatory and scientific standards. We are committed to editorial independence from our advertising partners.

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Personal FinanceVietnam Tax & PayrollHealth Metrics & BMIApplied MathematicsBusiness LendingSMB Financial Planning
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