Age on Other Planets Calculator

Background.

A year is not a universal unit — it is the time one particular planet takes to go round the Sun, and every other planet has its own. This calculator takes the span between two dates and divides it by each planet's sidereal orbital period, so it tells you how many orbits Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune have each completed while you have been alive. It also gives the span in Martian sols, the mean solar days that mission clocks count, and how long until your next Martian birthday.

One result is worth reading carefully, because it looks like a bug and is not. For a span of exactly 36 calendar years the Earth row reads 35.9994 orbits, not 36. That is correct: an orbit of the Sun measured against the fixed stars takes 365.2564 days, while the Gregorian calendar averages 365.2425 days per year, so calendar birthdays creep very slightly ahead of actual orbits. This page reports orbits, not calendar age. If you want your age in years, months and days, use the Age Calculator instead — this one is about celestial mechanics.

The orbital periods come from NASA JPL's Planetary Physical Parameters table and are sidereal periods, measured against the stars rather than against the moving equinox. That distinction matters: NASA's widely reproduced planetary fact sheet quotes tropical periods for some planets, which are shorter — Saturn's tropical period is about twelve days less than its sidereal one. Everything here comes from one table so the set is internally consistent, and that consistency is checked against a completely separate JPL dataset using Kepler's third law.

The Martian sol is not typed in either. It is derived from two other numbers on the same JPL page, the sidereal rotation period and the orbital period, through the relation that one solar day is slightly longer than one rotation for a prograde planet. The result, 1.02749125 Earth days, is the published sol length.

What is age on other planets calculator?

Your age on another planet is the number of times that planet has orbited the Sun since you were born. Because orbital periods differ enormously — Mercury takes 88 Earth days and Neptune takes 165 Earth years — the same lifetime translates into wildly different numbers.

The periods used here are sidereal orbital periods: one complete circuit measured against the distant stars. They differ slightly from tropical periods, which are measured against the moving equinox, and from the calendar year, which is an approximation chosen to keep the seasons in place.

A sol is a Martian mean solar day, the time from one Martian noon to the next: 1.02749125 Earth days, about 39 minutes longer than an Earth day. Mars missions run on sols rather than Earth days, which is why rover ages are quoted in them.

How to use this calculator.

1. 01Enter the birth date, or any start date you like.
2. 02Enter the date to count up to — usually today.
3. 03Read the total days: everything else is that number divided by an orbital period.
4. 04Read the Earth row as orbits completed, not as your calendar age.
5. 05Check the Mars sol count and the countdown to your next Martian birthday.

The formula.

Each planet's count is one division: the span in days divided by that planet's sidereal orbital period in days. The periods are JPL's, given in Julian years of exactly 365.25 days and converted here.

Work through the default. From 1990-07-29 to 2026-07-29 is 13149 days — 36 × 365 plus nine leap days, and the same figure comes out of subtracting the two Julian Dates. Dividing gives 149.4726 Mercury orbits, 58.5178 Venus orbits, 35.9994 Earth orbits, 19.1403 Mars orbits, 3.0347 Jupiter orbits, 1.2225 Saturn orbits, 0.4285 Uranus orbits and 0.2185 Neptune orbits. In Martian sols that span is 13149 ⁄ 1.02749125 = 12797.189, and the twentieth Martian birthday arrives 20 × 686.9796 − 13149 = 590.59 Earth days later.

HOW THE PERIODS ARE CHECKED. They come from JPL's Planetary Physical Parameters table. JPL separately publishes Keplerian elements — semi-major axes, from Standish and Williams — which never mention periods at all. Kepler's third law links the two: for a body of negligible mass, the period in years is the semi-major axis in astronomical units raised to the power 1.5. The four inner planets match to better than one part in ten thousand, Mars to better than one part in a million. The four giants sit systematically high by a few parts in ten thousand, and that is not an error either: the harmonic law drops the mass term, and Jupiter is a thousandth of the Sun's mass. The test suite asserts that residual is positive as well as small, so a mistyped period or a sign error would fail.

SIGNIFICANT FIGURES. The periods are known to eight significant figures, so the arithmetic contributes nothing. Treat four or five figures as meaningful; beyond that you are quoting the precision of a definition rather than of an age.

INVALID DOMAIN. Both dates must be real Gregorian dates, so 29 February 2024 is accepted and 29 February 2025 and 29 February 1900 are not. A reference date earlier than the birth date is rejected with the shortfall quoted back rather than returning a negative number of orbits.

A worked example.

Frequently asked questions.

References& sources.

1. [1]NASA JPL Solar System Dynamics, 'Planetary Physical Parameters'. Verified by retrieval 2026-07-29: the Sidereal Orbital Period column for all eight planets (Mercury 0.2408467 y through Neptune 164.79132 y) and Mars's sidereal rotation period of 1.02595676 d, referenced there to [B] 1992 and [D] 2018. Source of every constant on this page. Open access.
2. [2]NASA JPL Solar System Dynamics, 'Approximate Positions of the Planets' (Standish, E.M. & Williams, J.G., 1992), Table 1: Keplerian elements valid 1800–2050, semi-major axes from Mercury 0.38709927 au to Neptune 30.06992276 au. This is a separate dataset that never tabulates periods; it is used here as the independent cross-check, via Kepler's third law, on the periods above. Open access. Retrieved 2026-07-29.
3. [3]International Astronomical Union: the Julian year of exactly 365.25 days (31 557 600 s), the unit in which JPL expresses the orbital periods used here. Bibliographic reference to the IAU system of astronomical constants.