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Gregorian to Julian Converter

Convert Gregorian to Julian dates instantly with our free online calculator. Get Julian day numbers, calendar differences, and today’s Julian date in seconds.

Day of the month (1-31)
Select the month
Gregorian year (CE/AD)
Choose calculation method
Choose output format

Time can feel like a puzzle. We live by the Gregorian calendar, but many fields like astronomy, history, and even the military still use the Julian calendar.

That’s where our Gregorian to Julian Calculator comes in handy. With it, you’ll easily convert any Gregorian date to its Julian match. No guessing, no confusion just quick and accurate results.

What is the Gregorian to Julian Calculator?

Our tool takes your chosen Gregorian date and shows the equivalent Julian date. It also gives the Julian Day Number (JDN), which is a continuous count of days used by astronomers.

This way, you’ll see not only the date conversion but also how many days the Julian calendar lags behind the Gregorian one.

How to Use the Calculator

Using the calculator is simple.

  1. Pick a day, month, and year.
  2. Hit the convert button.
  3. See the results in both Gregorian and Julian formats.

You’ll also get the Julian Day Number, the calendar difference, and even a step-by-step breakdown of the math used.

The Formula Behind the Conversion

Don’t worry it looks complex, but we’ll keep it simple.

To go from Gregorian to Julian Day Number:

a = floor((14 - M) / 12)  

y = Y - a  

m = M + 12a - 3  

JDN = d + floor((153m + 2)/5) + 365y  + floor(y/4) - floor(y/100) + floor(y/400) + 1721119

Where:

  • d = day
  • M = month
  • Y = year

Then to get back to the Julian calendar:

a = JDN + 1524  

b = floor((a - 122.1)/365.25)  

c = floor(365.25 × b)  

d = floor((a - c)/30.6001)  

day = a - c - floor(30.6001 × d)  

month = d - 1  

year = b - 4716

This may look like rocket science, but our tool does the math for you.

Why Do You Need a Julian Converter?

Historians use it to read old records.

Astronomers rely on it for precise time tracking.

The military even uses a three-digit Julian date for quick daily logs.

So whether you’re checking Julian date today or comparing events in history, this converter is your go-to.

Which Came First, Julian or Gregorian?

The Julian calendar came first, introduced by Julius Caesar in 45 BC. But it ran slightly slow off by about 11 minutes each year. Over centuries, that drifted seasons out of sync.

Pope Gregory XIII fixed the issue in 1582, giving us the Gregorian calendar we use today.

Final Verdict

The Gregorian to Julian Calculator makes tricky calendar math easy. You don’t need to crunch formulas or scratch your head over history. Just enter your date, click convert, and get the answer.

It’s quick, free, and reliable. Whether you’re a student, researcher, or just curious, this tool will give you the Julian date you need.

FAQs

What is the Julian date today?

It’s the current day expressed in Julian format. Our calculator shows it instantly.

What’s the formula to convert Gregorian to Julian date?

The formulas above are used. Our tool applies them automatically.

Is the calculator free?

Yes, it’s 100% free to use.

What’s a Modified Julian Date?

It’s a shorter version of the Julian Day Number, often used in space science.