---
id: jdcal
version: "1.4.1"
license: BSD
license_treatment: permissive
maintenance: abandoned
---

# jdcal — Julian dates from proleptic Gregorian and Julian calendars.

License: permissive · Maintenance: abandoned · Downloads: 3.8M/mo

## What it is and what it does

jdcal is a pure-Python library for converting between Julian dates and calendar dates in both the Gregorian and Julian calendar systems. It stores Julian dates as pairs of floating-point numbers to preserve precision when working with large date values, allowing the integer and fractional parts to be handled separately for maximum accuracy in astronomical and scientific calculations.

The package provides functions to convert Gregorian or Julian calendar dates to Julian dates and back, test for leap years, and access module-level constants for the Modified Julian Date epoch and J2000.0. All conversions are proleptic, meaning they work for dates outside the historical range where each calendar was actually in use. With no runtime dependencies and a small footprint, it is suitable for embedded use in scientific applications, but the package has been abandoned since 2019 and will not receive updates.

Use it for:

- Astronomical calculations that require Julian dates for precise time representation across centuries.
- Converting historical or future calendar dates to Julian dates for scientific simulations or data analysis.
- Testing leap-year logic or validating calendar conversions in applications that handle diverse date formats.
- Splitting date precision across two numbers when working with systems that require high-precision time tracking.
- Proleptic calendar conversions for dates before the Gregorian calendar reform or in non-standard historical contexts.

## Worth the install?

AI-flagged interpretation of the facts above — verify before relying.

Converts between Julian dates and Gregorian or Julian calendar dates, storing Julian dates as pairs of floating-point numbers for maximum precision.

Yes, if you need Julian date conversion and can tolerate an abandoned package. The library is mature, has no dependencies, and works across Python 2 and 3. However, be aware that it will not receive bug fixes or updates—verify that its behavior matches your requirements before committing to it in a production system.

## Install

pip install jdcal
uv add jdcal
poetry add jdcal

## Installing jdcal

Before you install: Installation is straightforward with no runtime dependencies. However, the package is abandoned—last release was in April 2019 and last commit in February 2022—so it will not receive updates or security patches.

License in practice: Released under BSD (permissive license), so you can use, modify, and distribute it freely with minimal restrictions.

Quickstart:

pip install jdcal

from jdcal import gcal2jd, jd2gcal, is_leap

# Convert Gregorian date to Julian date
jd = gcal2jd(2000, 1, 1)
print(jd)  # (2400000.5, 51544.0)

# Convert back to Gregorian
gcal = jd2gcal(2400000.5, 51544.0)
print(gcal)  # (2000, 1, 1, 0.0)

# Check leap year
print(is_leap(2000))  # True

Verify before relying:

- Whether the abandoned status and lack of recent maintenance pose a risk for your use case, particularly if you rely on calendar edge cases or need Python 3.8+ support.
- Whether the proleptic calendar behavior (working for dates outside the calendar's historical validity) matches your application's requirements.

## Package facts

- License: BSD (permissive)
- Python support: unspecified
- Install friction: low
- Maintenance: abandoned
- Downloads: 3.8M/month (top 5,000 on PyPI)
- Known vulnerabilities: none known

## Tags

julian date conversion, gregorian to julian date, calendar date conversion, astronomical date calculations, modified julian date, leap year checker, proleptic calendar conversion, astronomy, date-conversion, calendar

[View on SkillFed](https://skillfed.io/packages/jdcal) · [View on PyPI](https://pypi.org/project/jdcal/)