Julian Date Calculator 4+


Designed for iPhone

    • 4.0 • 2 Ratings
    • $0.99

iPhone Screenshots


Calculate the Julian Date from Gregorian Calendar Date or vice versa. A small but useful tool for the Space Mission Analyst.

The Julian Date Calculator gives the user a simple and quick way to convert between Coordinated Universal Time (UTC) in the Gregorian Calendar to the Julian Date as well as the following selection of additional epochs and time systems:

- Modified Julian Date
- Modified Julian Date 2000
- GMAT Modified Julian Date
- Reduced Julian Date
- Truncated Julian Date (NIST and NASA)
- Dublin Julian Day
- Lilian Day Number
- ANSI Date
- Rata Die
- Unix Time
- GPS Time

The Julian date (JD) is the number of days and fractions of a day since noon January 1, 4713 BC at Greenwich. The Modified Julian Date (MJD) has an offset of 2,400,000.5 days from the Julian Date and hence starts at midnight November 17, 1858. The Julian Date is often used for scientific time measurement by the astronomy community and was introduced to provide a single system of dates that could be used when working with different calendars.

What’s New

Version 1.6

This app has been updated by Apple to display the Apple Watch app icon.

Updated for iOS 11.0.
- Modified Julian date 2000: Its initial epoch is at noon (12:00) proleptic Coordinated Universal Time (UTC) on January 1, 2000. It is commonly used in the space industry.
- GMAT Modified Julian Date: Its initial epoch starts at noon (12:00) proleptic Coordinated Universal Time (UTC) on January 5, 1942. It is used in the General Mission Analysis Tool developed by NASA.
- Leap seconds introduced June 30th 2015 and December 31st 2016

Ratings and Reviews

4.0 out of 5
2 Ratings

2 Ratings

J5thwheel ,

Works very well on iPhone5

It would be perfect for me if it would have three more functions:
- Display a third UTC seconds "wheel"
- Allow entry and display of GPS time in hexadecimal notation
- display current leap-seconds. That display could display number in effect when displaying historical time, or disappear when not displaying current time.
With those changes it would be worth more than $0.99 to me.

Universe Observer ,

Very Limited Usability

18 Dec 2022

I was hoping for a much better calculator with cleaner and better functionality than just being able to enter a date an time to get JD or any other time format. The value add that is missed here are:

(1) The ability to enter current local rime without having to compute the UTC. It’s a calculator and that is very basic functionality.

(2) The ability to be able to copy any field so that it can be pasted to a user’s astronomy log and/or observations made for AAVSO.

Nine years after the original app was offered and at least these two things should have been incorporated. I can only give it three stars at this point. It is time to correct the basic functionality that should have been there all along.

App Privacy

The developer, CosmoWerx, has not provided details about its privacy practices and handling of data to Apple.

No Details Provided

The developer will be required to provide privacy details when they submit their next app update.


  • Family Sharing

    Up to six family members can use this app with Family Sharing enabled.

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