This guide walks through the complete process of calculating a natal chart manually, using traditional astronomical tables and the Whole Sign House system.
You will need the following reference materials:
Used to find planetary positions at 00:00 GMT on each date.
Recommended:
Used to determine the Ascendant and Midheaven (MC).
Recommended:
Used to convert local birth time into Greenwich Mean Time (GMT).
Recommended:
All traditional astrological tables are calculated relative to Greenwich Mean Time.
If DST was in effect at the birthplace on the date of birth:
Add the time zone offset.
Example:
Birth Time: 3:00 PM EST
EST = GMT -5
3:00 PM + 5 hours = 8:00 PM GMT
Subtract the time zone offset.
Example:
Birth Time: 20:05 Romania (GMT +2)
20:05 - 2 hours = 18:05 GMT
Result:
GMT Birth Time = 18:05
Sidereal Time measures the rotation of the Earth relative to the fixed stars and determines which zodiacal degree is rising.
Look up the birth date in the ephemeris.
Record the value listed as:
Sidereal Time
Add the GMT birth time to the ephemeris Sidereal Time.
Example:
ST at 00:00 GMT = 11h 12m
GMT Birth Time = 18h 05m
Total = 29h 17m
If the result exceeds 24 hours:
29h 17m - 24h = 5h 17m
Earth rotates approximately:
1° longitude = 4 minutes of sidereal time
Calculate:
Longitude × 4 minutes
Example:
Longitude = 26.7° East
26.7 × 4 = 106.8 minutes
= 1h 46m 48s
Add the correction.
LST = ST + Longitude Correction
Subtract the correction.
LST = ST - Longitude Correction
East is Ahead → Add
West is Behind → Subtract
Open the Table of Houses.
Locate:
Read the value under:
ASC
This gives:
Example:
7° Gemini
On the same row, locate:
MC
or
10th House
This gives the Midheaven degree.
Example:
22° Aquarius
In Whole Sign Houses:
Ascendant:
7° Gemini
House structure:
| House | Sign |
|---|---|
| 1st | Gemini |
| 2nd | Cancer |
| 3rd | Leo |
| 4th | Virgo |
| 5th | Libra |
| 6th | Scorpio |
| 7th | Sagittarius |
| 8th | Capricorn |
| 9th | Aquarius |
| 10th | Pisces |
| 11th | Aries |
| 12th | Taurus |
The MC remains at its actual zodiacal degree.
Therefore, in Whole Sign houses, the MC may fall in:
Mark the MC exactly where its sign falls.
Ephemerides normally list planetary positions at 00:00 GMT.
Since planets move during the day, you must calculate their exact positions at birth.
Subtract the position on the birth date from the position on the following date.
Example:
Venus Day 1 = 10°15' Libra
Venus Day 2 = 11°27' Libra
Daily Motion = 1°12'
Divide GMT birth time by 24 hours.
Example:
Birth Time = 18:05 GMT
18.08 ÷ 24 = 0.753
Multiply daily motion by the fraction of the day.
Example:
1°12' × 0.753
≈ 54'
10°15' + 54'
= 11°09' Libra
This is the planet’s natal position.
Use a circular chart divided into 12 equal 30° sectors.
Place the Ascendant sign at the left side of the wheel:
9 o'clock position
This is the First House.
Label the remaining signs counter-clockwise.
For each planet:
Example:
Mars 17° Leo
→ Plot in Leo sector
→ Approximately halfway through the sign
Mark the Midheaven at its exact degree.
Remember:
Connect planets that are approximately:
| Aspect | Separation |
|---|---|
| Conjunction | 0° |
| Sextile | 60° |
| Square | 90° |
| Trine | 120° |
| Opposition | 180° |
Draw aspect lines through the center of the chart.
Before accepting the chart:
☐ DST corrected
☐ Local time converted to GMT
☐ Ephemeris ST copied correctly
☐ GMT time added correctly
☐ Longitude correction applied correctly
☐ East longitude = ADD
☐ West longitude = SUBTRACT
☐ Ascendant sign used as entire 1st house
☐ Houses labeled counter-clockwise
☐ Daily motion calculated
☐ Interpolation completed
☐ Planets plotted at correct degrees
☐ MC marked separately from house boundaries
The most frequent mistake is applying the longitude correction in the wrong direction.
Remember:
East is Ahead → Add
West is Behind → Subtract
If you obtain an obviously impossible Ascendant (for example, one that is inconsistent with the solar position and time of day), the first thing to check is the sign of the longitude correction.