The Comparison of the Methods for Applying Intercalary in Solar Hijri Calendar in Different References

From the year 1926/1305, Solar Hijri Calendar is used in Iran as the official calendar. In this calendar, each year is consisted of 12 months which 6 of them have 31 days. Next 5 months have 30 days and the 12th month has 29 days. Just in Intercalary years, the 12th month has 30 days. The base of the Solar Hijri Calendar is the time when the prophet of Islam traveled from Mecca to Medina in the 7th century. Solar Hijri calendar can be assumed as the most exact calendar ever exists in the world. One of the reasons caused this calendar to be so exact is that there is Intercalary years in this calendar, which have years distance to meet next Intercalary year. This is different from the other solar calendars which have 4 years duration for Intercalary years. But there is no explicit rule to when to apply these 5 years durations for Intercalary years.This caused the past and the present scientists, who studied about this calendar, present different ideas about how to apply Intercalary duration. In this study we try to review a report about the methods, presented by past scientists and after that we present currently scientist ideas about Intercalary calculation tables. As our view this study will help us to compare different scientist’s theories and to find which one is more exact.