How Are These Dates Calculated?
Every date on this site is calculated from planet positions, using the tropical zodiac and Placidus houses (Whole Sign where Placidus cannot be drawn, near the poles). We test the results against Swiss Ephemeris, a widely used astrology reference, and publish how close they come.
How close the dates are
Swipe sideways to see the whole table
| What we compared | Sample | Result |
|---|---|---|
| Saturn return exact dates | 10,495 passes | 2 fell on a different UTC date |
| Solar return moment | 4,980 returns | Largest gap 30.3 seconds |
| Retrograde start and end dates | 4,054 turning points | 2 fell on a different UTC date |
| Transit exact dates | 281,883 passes | 67 fell on a different UTC date |
| Rising sign, midheaven and house cusps | 29,332 charts | No sign differed |
| Sun to Pluto, by sign | 24,002 moments | No sign differed |
| Planet in house | 180,000 placements | 3 differed |
| North Node, by sign | 24,002 moments | 1 differed |
Tested for dates from 1900 to 2100. Dates outside that range are not calculated. Date differences happen when a pass falls within seconds of midnight, or when a planet is moving very slowly.
Definitions we use
Saturn return. Exact is the moment Saturn reaches the longitude it held at your birth. The window starts and ends when Saturn is within 5 degrees of that spot. We also give the time Saturn spends in your birth sign. You can change the 5 degrees on your result.
Unknown birth time. We calculate both ends of your birth day and tell you how much your dates could move. Without a time we leave out the rising sign, the houses and the Moon's exact position.
Transits. A transit counts when a planet is within 1 degree of an exact conjunction, sextile, square, trine or opposition to a point in your chart.
Retrograde and shadow. A retrograde runs between the two moments a planet appears to stop. The shadow period starts when the planet first reaches the degree where it will turn direct, and ends when it returns to the degree where it turned retrograde.
Time zones. Your birth place gives your time zone, including daylight saving at the date you were born. Dates you see are converted to your current time zone.
Where the data comes from
Planet positions come from Astronomy Engine with corrections from NASA JPL Horizons. City names, coordinates and time zones come from GeoNames, used under the CC BY 4.0 licence. Dates after 2026 include an estimate of how the Earth's rotation will change, which no one can measure in advance.
The meanings on this site are written from long-established astrology books and reference works. Astrology is a tradition for reflection. It has no scientific evidence behind it, and nothing here is medical, legal or financial advice.