How to Calculate Your Solar Arc Directions (Step by Step)

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This page is the working method for solar arc directions. It turns your age into a solar arc, adds that arc to your natal planets and finds when a directed planet reaches an exact aspect to a natal planet. What the technique is, the choice of key and how contacts are read are covered on solar arc directions.

Solar arc directions are a separate symbolic directing technique, not a transit. You will not look up today's sky at all: the only ephemeris reading is the Sun a few weeks after your birth.

Do-it-yourself method. Astrologist.com does not calculate solar arcs. The free birth chart gives the positions for whatever date, time and place you enter, and it does not turn your birth data into a progressed chart, a solar arc, directed positions, directed angles or a list of direction contacts. In Step 3 you can enter the progressed instant you work out by hand into that ordinary chart to read the Sun. The example figures were calculated offline with the same routines (see the methodology page) and are a check on your arithmetic. Ask the Astrologist does not receive degrees, arcs or directed positions and cannot calculate them for you.

You need your natal chart with a birth time, the free chart or a Tropical ephemeris, and about half an hour.

Steps 1 to 3: find your progressed Sun

These three steps are the start of the secondary-progressions method, so they are kept short here. How to calculate your secondary progressions explains each one in full.

1. Write your birth instant in Universal Time (UT), allowing for the time zone and any daylight saving in force that day (birth time, time zones and daylight saving).
2. Turn your age into a progressed instant. For a whole-number age N, add N days to the birth instant and keep the same UT clock time.
3. Read the Sun at that instant, from an ephemeris or from the free chart. The free chart takes local civil time, so convert the progressed UT instant to the civil time in force at your birthplace on the progressed date, which may not be the offset you were born under. Read only the Sun from that chart.

Step 4: subtract to get the arc

Solar arc = progressed Sun minus natal Sun, measured forward around the zodiac. To subtract across sign boundaries, turn each position into a longitude from 0° Aries first: add 30° for each sign before it (Aries 0°, Taurus 30°, Gemini 60°, and so on to Pisces 330°). If the result is negative, add 360°.

You can also note the two alternative keys for comparison: Naibod, your age multiplied by 0°59′08″, and the one-degree key, your age in degrees. They are explained on the concept page; the steps below use the true arc only.

Step 5: add the arc to each natal planet

Add the same arc to each of the ten natal planets from the Sun to Pluto and convert back to signs. Your directed Sun should equal the progressed Sun from Step 3, which is a useful check. Note any planet that has moved into a new sign.

The free chart shows whole minutes cut off from a slightly more precise value, so a hand sum can come out one minute different from a calculation that starts from the unrounded positions. That is normal and does not change the method.

Step 6: list directed-to-natal contacts

Compare each directed planet with each natal planet for the five major aspects: 0°, 60°, 90°, 120° and 180°. Keep anything within 1°. That ±1° is this guide's illustrative screening window, not an Astrologist.com orb or a rule every astrologer uses.

Skip directed-to-directed comparisons. Every planet moved by the same arc, so two directed planets are exactly as far apart as they were at birth.

Step 7: find the exact age

For a directed planet P making aspect A to a natal planet T:

1. List the target degrees. They are T + A and T − A, taken around the circle. A conjunction has one target; for an opposition the two calculations give the same point. A sextile, square or trine has two different targets, one on each side of T.
2. Work out the arc each target needs: target minus natal P, measured forward (add 360° if negative).
3. Keep the target whose required arc falls in the age range you are looking at. The other one usually needs an arc decades away.
4. Find the age. Repeat Steps 2 to 4 for the next birthday to get the arc a year later. The required arc lies between the two; the fraction of the year's growth it represents gives the fraction of the year.
5. Turn the age into a date by counting age × 365.2422 days from the birth date, and give it as early, mid or late in the month. One minute of arc is about six days of life, so positions read to the minute cannot support a finer date.

Worked example: Lotte at 35

Lotte is a fictional example chart used on this site: Utrecht, 27 August 1991, 06:55 CEST, a recorded time. Her age was fixed at 35, the age she is on 31 October 2026, before any contact was looked at.

Steps 1 to 3. Utrecht was on summer time (CEST, UT+2) on her birth date, so the birth instant is 04:55 UT. Age 35 means 35 days later: 1 October 1991, 04:55 UT. By then summer time had ended, so the local civil time in Utrecht was 05:55 CET (UT+1), not 06:55. Entering 1 October 1991, 05:55, Utrecht in the free chart gives a progressed Sun of 7°31′ Libra. Reusing 06:55 would give 7°34′ Libra, an hour's worth of solar motion too far.

Step 4. 7°31′ Libra is 187°31′; her natal Sun, 3°26′ Virgo, is 153°26′. The arc is 187°31′ − 153°26′ = 34°05′ (34.08° unrounded). For comparison, Naibod gives 34°29′ and the one-degree key 35°.

Step 5.

With an arc of more than 30°, all ten planets now sit in the next sign. Directed Venus, Mars and Jupiter crossed less than a degree ago, so they are worth checking carefully. Calculated from unrounded positions, directed Mars is 0°49′ Scorpio rather than 0°50′: the one-minute rounding difference described in Step 5, still in Scorpio.

Step 6. Within the ±1° window at her 35th birthday:

• Directed Mars square natal Saturn, 0.55° before exact.
• Directed Venus trine natal Saturn, 0.72° before exact.
• Directed Jupiter trine natal Saturn, 0.75° before exact.
• Directed Neptune square natal Pluto, 0.50° after exact; it was exact at 34.49, mid February 2026.

From the displayed minutes the Mars square looks 32′ (0.53°) wide; the calculated 0.55° is the small display difference again.

Step 7, for directed Mars square natal Saturn. Natal Saturn 1°22′ Aquarius is 301°22′. The two targets are 301°22′ + 90° = 31°22′ (1°22′ Taurus) and 301°22′ − 90° = 211°22′ (1°22′ Scorpio). Natal Mars, 26°45′ Virgo, is 176°45′. The Scorpio target needs 211°22′ − 176°45′ = 34°37′ of arc; the Taurus target would need 214°37′, about two centuries away. So the target is 1°22′ Scorpio.

At 36 the progressed instant is 2 October 1991, 04:55 UT (05:55 CET), the progressed Sun is 8°30′ Libra and the arc is 35°04′. The arc grows 59′ this year, and 34°37′ is 32′ past 34°05′, so the age is about 35 + 32/59 = 35.54. Solved from the unrounded positions it is 35.55: about 0.55 × 365 ≈ 201 days after her 35th birthday, mid March 2027.

The full list for her 36th year:

Her August chart runs behind Naibod (34.08° against 34.50° at 35), so Naibod dates these contacts about five months earlier than the true arc, and the one-degree key almost a year earlier. Ruben's January chart, on the concept page, runs ahead of Naibod, so for him the shift goes the other way. Neither direction makes a key right or wrong.

Read each contact as a theme coming into focus around those months, with the meaning set by the planets involved, not as an event on a date.

Step 8: test the birth time

Run the whole method again for a birth time an hour earlier and an hour later, recalculating both the natal planets and the progressed Sun from each candidate time. For Lotte the same three contacts stay in her 36th year, but the dates move:

The arc barely changes with the birth time; the natal positions do, the Moon most of all, at about half a degree an hour. A contact to the natal Moon can shift by months for an hour's difference.

Without a birth time: do not use noon, or any single time, as your birth time. A contact between two planets other than the Moon can be stated only if you check it at close intervals through the entire possible birth-time range (not just the start and end of the day) and it stays the same contact in the same date band throughout; otherwise mark it unresolved. Contacts to or from the Moon, houses and angles are not available without a reliable time. How to read a chart without a birth time covers what else survives.

Houses and angles are not part of this method. If you have a reliable birth time and exact natal cusp degrees from a source that prints them, you can place directed planets in your natal houses as a separate overlay; how to find your house cusps explains the cusp degrees. Directed angles are described as a concept on the concept page only.

Common mistakes

• Adding your age in degrees and calling it the true arc. That is the one-degree key, a different convention.
• Reusing your local birth time on the progressed date. If the clock offset changed, as it did for Lotte, the progressed Sun is off by a few minutes of arc, and every directed position with it.
• Moving only one planet. The technique adds the same arc to every included planet.
• Treating directed-to-directed aspects as new. They are your natal aspects.
• Reading the rest of the free chart for the progressed date. Its Moon, planets, houses, angles and aspects belong to that ordinary chart, not to solar arcs; only the Sun is used.
• Choosing the wrong square, sextile or trine target. Check both targets and keep the one whose required arc fits the ages you are looking at.

Next steps

What the arc means and how the keys differ is on solar arc directions, with Ruben's chart at 33. The progressed Sun comes from how to calculate your secondary progressions, and secondary progressions explained compares the two techniques' starting point. For real-sky timing with an ephemeris, see how to read transits without a tool. Get your natal positions from the free birth chart, and you can ask the Astrologist about directed positions you have worked out yourself.

Related articles

• Solar Arc Directions
• How to Calculate Your Secondary Progressions
• Birth Time, Time Zones and Daylight Saving
• How to Read a Chart Without a Birth Time
• How to Find Your House Cusps
• How to Read Transits Without a Tool