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Julian Date converter

Convert a calendar date and time to the astronomical Julian Date (JD) and back, live. It also returns the Modified Julian Date (MJD = JD − 2400000.5) and the Unix timestamp, and lets you pick the Gregorian or Julian calendar for dates before the 1582 reform. Astronomer-grade: noon UTC on 1 January 2000 comes out to exactly JD 2451545.0.

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Open Julian Date converter and you get an answer straight away, with no account to create. You will find it under Dates & time, with Add or subtract days from a date and Date Calculator for the neighbouring cases.

How to use it

  1. Open the tool — no signup or install needed.
  2. Enter your input or adjust the available options.
  3. Get your result instantly, then copy or download it.

Frequently asked questions

What does Julian Date converter do?

Convert a calendar date and time to the astronomical Julian Date (JD) and back, live. It also returns the Modified Julian Date (MJD = JD − 2400000.5) and the Unix timestamp, and lets you pick the Gregorian or Julian calendar for dates before the 1582 reform. Astronomer-grade: noon UTC on 1 January 2000 comes out to exactly JD 2451545.0.

What does a concrete case look like?

2000-01-01 12:00 UT → JD 2 451 545,0 (J2000.0) — the tool shows every step in between, not just the final figure.

When would I actually use this?

Answering a scheduling question exactly: how many working days until a deadline, what date falls sixty days out, and what time that is for a colleague elsewhere.

What is the most common mistake?

Counting days by subtracting dates and forgetting whether the endpoints are included. Inclusive and exclusive counts differ by one, which is the difference between meeting a deadline and missing it.

How is Julian Date converter different from Add or subtract days from a date?

They sit next to each other but answer different questions: Add or subtract days from a date is the one to open when you need it to find the date a number of days before or after a starting date. Pick whichever matches what you're starting from — both are free.

Is there a tool for the next step?

Date Calculator is the closest one after this: Add or subtract years, months, weeks and days from any date, with a business-day mode and explicit month-end clamping.

What else is worth having open alongside it?

Date difference calculator and Date Pattern Generator — they come up in the same task often enough to be worth a second tab.

Where do the figures come from?

Calendar arithmetic follows the proleptic Gregorian calendar and the IANA time-zone database, so daylight-saving transitions and leap years are handled. Public holidays vary by country and region and are not assumed.

Further reading

All guides →
How-toHow to Add or Subtract Days from a DateCount forward to add, backward to subtract, rolling over month ends. Here's how, why month lengths and leap years trip you up, and when weekends count.How-toHow Many Days Until a Date? (With Worked Examples)Count the days until any future date, understand inclusive vs. exclusive counting, and build an accurate countdown you can trust.ExplainerSeconds, Minutes and Hours: How Time Units Fit TogetherThe relationships behind 60 seconds, 60 minutes, 24 hours and 86,400 seconds a day, with quick conversions you can reuse.How-toHow Many Days Until My Birthday? (Step by Step)Find the exact days to your next birthday, including the tricky case where this year's date has already passed.ExplainerWhat Is a Leap Year? The /4, /100, /400 Rule ExplainedWhy some years have a February 29, how the divisible-by-4, -100 and -400 rules combine, and how to check any year quickly.How-toHow Many Weeks Until a Date? (With Worked Examples)Count the weeks between today and any future date. Learn the simple divide-by-seven method, when to round, and the difference between inclusive and exclusive counting.