Find the longitude for the location of your birth. Multiply the number of degrees by 4 minutes. For example, if you were born at 95 degrees west, the result is 6 hours 20 minutes.
Add the result from above to the local time of your birth if you were born in a western longitude. Subtract the above result from the local time of your birth if you were born in an eastern longitude. For example, if you were born at 2:00 PM at 95 degrees west then the Greenwich Mean Time (G.M.T.) is 8:20 PM.
Find the correction for which the time of birth in G.M.T. is past noon. For example, if you determined the G.M.T. for your birth to be 8:20 PM then the correction is 8 hours 20 minutes past noon.
Divide the number of hours by two. Record the result in months. For example, 8 hours divided by 2 equals 4 months. Estimate ½ month as 15 days.
Divide the number of minutes by 4. Record the result in days. For example, 20 minutes divided by 4 equals 5 days.
Subtract the months and days calculated above from your date of birth. For example, if you were born at 8:20 PM G.M.T. on April 24, 1991 then the correction is 4 months and 5 days. April 24, 1991 minus 4 months and 5 days gives the adjusted calculation date of December 19, 1990.