Davison Chart Calculator

Written by Orbitarot · Sources: our own engine, positions checked against NASA JPL Horizons (method); place data GeoNames (CC BY 4.0); interpretations our own · Updated October 7, 2026

What a Davison chart is

The British astrologer Ronald Davison described this method in his 1977 book on synastry. Instead of averaging planet positions, as a composite chart does, he averaged the two moments in time and the two places on Earth, then cast an ordinary chart for that midpoint. Because the result is a real moment, the planets in a Davison chart stand in positions the sky actually showed, with real speeds, retrogrades and Moon phase, and the chart can be followed by transits like any birth chart.

How a Davison chart is calculated, with an example

Take one person born at noon on 1 January 1990 in London and another born at noon on 1 January 1994 in New York.

1. Time midpoint. In Universal Time the births are 12:00 on 1 January 1990 and 17:00 on 1 January 1994 (New York noon is five hours behind). They are 1,461 days and 5 hours apart, so the midpoint is 730 days, 14 hours and 30 minutes after the first birth: 02:30 UT on 2 January 1992.
2. Place midpoint. London is at about 51.5 degrees north, 0.1 degrees west; New York about 40.7 north, 74.0 west. The simple average is about 46.1 north, 37.1 west, a point in the North Atlantic.
3. The chart. The calculator then casts a normal chart for 02:30 UT on 2 January 1992 at that latitude and longitude, with the house system you chose.

A midpoint in the ocean is normal and does not matter: the chart only needs coordinates, not a town.

Simple average or great-circle midpoint

Astrologers do not agree on how to average two places. Davison's own method averages latitude and longitude separately, which is what most software does and what we use by default. Some prefer the true halfway point along the shortest path over the globe (the great-circle midpoint), which can be quite different for places far apart in longitude: for London and New York it lies at about 52.4 north, 41.3 west, about 760 kilometers from the simple average. The calculator lets you switch between the two and shows both locations.

For two births on opposite sides of the date line, averaging longitudes naively can put the midpoint on the wrong side of the planet. The calculator averages along the shorter way round.

Davison, composite and synastry

All three describe relationships. Synastry compares two charts contact by contact; the composite averages planet positions into a chart that never existed in the sky; the Davison averages time and place into a chart that did. Composite and Davison charts often share Sun and planet signs, but the Moon and the angles can differ a lot, because a few hours in time moves them a great deal. Some astrologers use both and read what they agree on.

Common Davison chart mistakes

• Wrong time zones. The midpoint must be taken in Universal Time, after each birth has been converted from its own local time. Averaging two clock times directly gives the wrong moment. The calculator converts both for you.
• Missing birth times. Without both times the midpoint moment is uncertain by up to a day, so the Davison Moon, Ascendant and houses cannot be trusted.
• Reading it as a forecast. Like every relationship chart, it describes themes, not how a relationship will turn out.

Questions

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