
When there are 30 days of Zul Hajjat ilHaraam (the last month of Hijri year) instead of its usual 29 days, in a Hijri Year then it is called as a Leap Year (Kabeesah). 1427 years have passed since Rasoolullaah (SAWS) migrated from Makkah to Madeenah. As per the ‘ Uloom and hidaayaat of Maulaana Ali (as) our A'immateTaahereen (AS) have calculated the days of a leap year in such a way that there is not even a difference of a single day till now. There are 11 leap years in a given period of 30 years. Beginning from the time of Hijrat (migration) of Rasoolullaah (SAWS), if we divide 1427 (hijri years passed till now) by 30 (no. of years for the cycle of 11 leap years to get complete) then we get 47 as a quotient i.e. till now the cycle of 30 years have been completed for 47 times. So the year 1427 is the 17 th year of 48 th 30 year cycle.
In every 30 year cycle, the 2nd , 5th , 8th , 10th , 13th , 16th , 19th , 21st , 24th , 27th and 29th year is always a leap year. 
Calculating according to above given values, if you want to know whether a year is a leap year or not, you have to divide the given year by 30. If the remainder value coincides with the number of the year above, then it is a leap year.
Example: You want to know whether 1423 was a leap year or not, then divide 1423 by 30. The remainder value is 13 which coincide with the number of year given above, hence 1423 was a leap year. Based on the above calculations, the years till 1500 A.H. which are leap years are given below:
1401, 1404, 1407, 1409, 1412, 1415, 1418, 1420, 1423, 1426, 1429, 1431, 1434, 1437, 1439, 1442, 1445, 1448, 1450, 1453, 1456, 1459, 1461, 1464, 1467, 1469, 1472, 1475, 1478, 1480, 1483, 1486, 1489, 1491, 1494, 1497, 1499. 
Astonishingly in every Hijri Year, there is an unbelievable coincidence of days and dates. As given in the table given below: 6th of Moharram ulHaraam and 1st of Ramzaan ulMo'azzam falls on the same day so as 4th of Safar ulMuzaffar and 1st of Ramzaan ulMo'azzam and so on in the other months. In the similar way 5th of Moharram ulHaraam and Yaume‘Arafah falls on the same day and so on in the other months.
1st of Ramazaan

Name of month 
Yaume‘Arafah 



6th 
Moharram ulHaraam 
5th 
4th 
Safar ulMuzaffar 
3rd 
3rd 
Rabi ulAwwal 
2nd 
8th 
Rabi' ulAakhar 
7th 
7th 
Jamaadi ulAwwal 
6th 
5th 
Jamaadi ulAakhar 
4th 
4th 
Rajab ul‘Asab 
3rd 
2nd 
Shabaan ulKareem 
1st 
8th 
Ramzaan ulMo'azzam 
7th 
6th 
Shawwal ulMokarram 
5th 
5th 
Zilqaad alHaraam 
4th 
10th 
Zilhajj ilHaraam 
9th 
It is being accounted from the HadeeseShareef of Rasoolullaah (SAWS) that,
4th of Rajab, 1st of Ramazaan and 10th of Zulhajj – Eid ulAzhaa falls on the same day so as 5th of Rajab, 23rd of Ramazaan and 18th of Zilhajj; and 6th of Rajab, 1st of Shawwaal – Eid ulFitr and 1st of Moharram falls on the same day. 
