How to use it
- Type the year you want, or leave the box empty to see this year.
- Read the table: each row is one retrograde, from the station where Mercury turns backward to the station where it turns direct again.
- Check the sign and degree of each station, and the two shadow columns if you follow astrology.
- Tick Show times in UTC if you want Universal Time instead of your own time zone.
How the stations are found
Mercury appears to move backward when its apparent longitude, seen from the Earth, decreases. The turning points are the stations. At a station the apparent speed is zero: the speed changes sign from positive to negative at the retrograde station and back at the direct station.
The calculator takes the apparent speed every day, looks for each change of sign, and then narrows each change down to one minute by bisection. The positions are geocentric, apparent and referred to the true ecliptic of date, which is the tropical zodiac used in astrology.
speed = (longitude at t + 6 h − longitude at t − 6 h) ÷ 0.5 day
A station is the moment when the speed changes sign.What the shadow periods are
The shadow periods come from astrological tradition. They are not astronomical events. Before a retrograde, Mercury, moving forward, first reaches the longitude where it will later turn direct, and that starts the pre-retrograde shadow. It lasts until the retrograde station.
After the retrograde, Mercury turns direct and moves forward through the same degrees again. The post-retrograde shadow ends when it reaches the longitude where it turned retrograde.
What this page does not show
- Mercury's visibility. It sits close to the Sun for much of the year and is hard to see, whatever its direction.
- Interpretations of any retrograde. Astrology assigns meanings to these periods; this page gives the dates and degrees only.
- Other planets. The page for all planets is the retrograde calendar.
Worked example: the retrograde that starts in Pisces in 2026
In 2026 Mercury turns retrograde at 06:47 UT on 26 February, at 22° 34′ Pisces, and turns direct at 19:34 UT on 20 March, at 8° 29′ Pisces. The retrograde lasts 23 days by the calendar count.
The pre-retrograde shadow begins on 11 February 2026 at 22:13 UT, when Mercury, moving direct, reaches 8° 29′ Pisces. The post-retrograde shadow ends on 9 April 2026 at 11:41 UT, when Mercury, moving direct again, reaches 22° 34′ Pisces.
Frequently asked questions
Does Mercury really move backward?
No. The planet keeps its orbit. It looks as if it reverses because the Earth passes it in its faster orbit, so its apparent position in the sky moves backward for a few weeks.
How often does Mercury go retrograde?
About three times a year, each time for roughly three weeks. A period that starts in late December or ends in early January is counted in the year where it starts or ends.
How exact are the times?
The stations are found to the nearest minute. The positions agree with the JPL Horizons ephemeris to a few thousandths of a degree in the checks made for this page.
Why are the shadow periods shown if they are not astronomy?
Because many people look them up. They are marked as tradition on the page, and their dates are computed the same way as the stations, so you can see exactly what they mean.
Can I see the times in my own time zone?
Yes. By default the times are in your device's time zone, with its name. Tick Show times in UTC to see Universal Time instead.
Sources
- JPL Horizons, NASA's ephemeris system: the geocentric Mercury positions used to check the longitudes
- astronomy-engine, the open-source astronomy library (MIT) that computes the positions
- Farmers' Almanac: Mercury retrograde dates, a published list used to check the dates
Figures and text last checked on Tuesday, November 10, 2026.