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Sanfu (Dog Days) Calculator

Date & Time

Dog days & Shujiu dates, Geng-day algorithm

Quick Answer

Sanfu (Dog Days) Calculator: Dog days & Shujiu dates, Geng-day algorithm. Sanfu (Dog Days) Calculator uses standard date & time formulas to compute accurate results instantly.

Supports 2020-2030 (verified astronomical data)

2026 Dog Days (Sanfu)
40 days
7/15 – 8/23 · Extended mid-fu (20 days)
Chu-fu (1st)7/15 ~ 7/24
Zhong-fu (20d)7/25 ~ 8/13
Mo-fu (last)8/14 ~ 8/23

Calculation steps

  1. 12026 Summer Solstice: Jun 21
  2. 2The 3rd Geng (庚) day after Summer Solstice = 7/15 → Chu-fu starts (Ganzhi of the day: 庚寅)
  3. 3The 4th Geng day = 7/25 → Zhong-fu starts
  4. 4The 1st Geng day after Autumn Begins (Aug 7) = 8/14 → Mo-fu starts
  5. 5Zhong-fu length = Mo-fu start − Zhong-fu start = 20 days → total 40 days

Sanfu in nearby years

YearChu-fu startsMid-fu daysTotal
20247/152040
20257/201030
20267/152040
20277/201030
20287/142040
Why 30 or 40 days? Chu-fu and Mo-fu are always 10 days (one Geng cycle). Zhong-fu runs from the 4th Geng day after Summer Solstice to the 1st Geng day after Autumn Begins — 10 days in some years, 20 in others. A 20-day Zhong-fu occurs when there are 5 Geng days between the two solar terms. Health tips: avoid midday sun, replenish water and electrolytes, and be cautious with "winter-disease summer treatment" (冬病夏治) claims — consult professionals.

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How to Use

  1. Pick dates or a mode: select start/end dates or switch modes in the Sanfu (Dog Days) Calculator.
  2. Instant calculation: results appear immediately with day/week/month equivalents.
  3. Solve both ways: change any field and everything updates — forward or reverse.
  4. Check the context: read the solar-term/holiday/rule notes on this page.

Key Points

  • Sanfu (Dog Days) Calculator is a free online date & time tool — open and use, no sign-up.
  • All calculations run locally in your browser; your data never leaves the device.
  • Key capability: Dog days & Shujiu dates, Geng-day algorithm.
  • Results come with formulas and reference tables so you can verify every number.

Formula & How It Works

Sanfu (Dog Days) Calculator formula

Sanfu (Dog Days) Calculator uses standard date & time formulas to compute accurate results instantly.

FAQ

How do I use the Sanfu (Dog Days) Calculator?
Open the page and fill in the input fields — results update automatically. Dog days & Shujiu dates, Geng-day algorithm.
Are the results accurate?
Yes. Standard formulas and conversion factors are used and verified.
Is it free? Do I need to sign up?
Completely free. No registration, login or download required.
Does it work on mobile?
Yes. The responsive design works on phones, tablets and desktops.
Is my data saved?
No. Everything runs locally in your browser.

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Source & Updates

Based on standard calendar arithmetic. Last updated: 2025-07

Authoritative sources:

Last updated:

Formulas and content on this page are reviewed by the YiJianSuan team. For reference only — official sources prevail.

Maintained and periodically reviewed by the YiJianSuan editorial team — review process in ourEditorial Policy.

Cite this page: YiJianSuan. Sanfu (Dog Days) Calculator[EB/OL]. https://www.yijiansuan.com/en/c/date/sanfu

Results provided by this tool are for reference only and do not constitute professional advice.