A return is a longitude equality
Take the apparent geocentric tropical ecliptic longitude of a planet at the recorded birth instant. Call that the natal target. At a later instant, calculate the moving planet in the same coordinate system. A return occurs when the two longitudes agree modulo 360°. The sign and degree may be repeated, but the rest of the sky is different. The calculator covers Mercury, Venus, Mars, Jupiter, and Saturn; solar and lunar returns have their own chart tools.
These are Earth-centered apparent positions, with light-time and aberration accounted for by the site’s local Astronomy Engine bundle. The tropical zodiac follows the equinox of date. Sidereal signs, heliocentric longitudes, or a different ephemeris can give different return times. No birthplace coordinates enter this planet-to-planet longitude equality, though a chart drawn for the moment does require a place to define its angles and houses.
Why three dates can all be real
A planet normally moves forward in zodiac longitude, then can appear to slow, reverse, and move forward again as seen from Earth. If the loop straddles its natal degree, the moving longitude crosses that target on the way forward, again on the way backward, and once more after turning direct. All three UTC instants satisfy the same return equation. Calling just the first crossing “the” return hides the repeat contacts; assigning only the final one is an interpretive convention, not a different astronomical calculation.
The table labels motion at each crossing. A crossing very near a station may be marked “near station” because a rounded minute and small speed make the direction unstable. A tangential touch exactly at a stationary extremum may not change sign across the target; this search is designed for crossings and may not list that rare contact. Longitudes are sampled at six-hour steps for Mercury and Venus, twelve hours for Mars, daily for Jupiter, and every two days for Saturn, then crossing intervals are refined numerically.
Reading the search interval
The input date starts at 00:00 UTC. The planet sets a practical look-ahead interval: two years for Mercury, three for Venus, five for Mars, fifteen for Jupiter, or thirty-three for Saturn. These are search windows, not claims that every planet returns at a fixed period. An interval can contain zero or many crossings. The date range stops at the calculator’s year-2100 limit; a late start may therefore show no crossing simply because too little time remains.
The exact birth time matters because the natal target moves even within a single day. The local clock reading must be converted using the UTC offset actually in force at the birth date and place, including historical daylight-saving changes. The result is UTC. To discuss a return in local civil time, convert each event with the rules for the chosen location and event date. Do not reuse the birth offset for future event dates.
What an astrologer may do next
Astrologers may read a return as a symbolic cycle point for the planet’s traditional topics. That interpretation is separate from the measured longitude match. A full return chart can be cast for any listed moment and a chosen location, then compared with the natal chart. Moving the return location changes its local horizon and houses, while the worldwide geocentric match remains at the same UTC instant. This page reports dates and positions, not predictions about a person’s decisions or events.