"A lunar year is 12 lunar months, so 19 of these would be 228 lunar months. With the 7 extra months, the total period would be 235 lunar months of 29.530589 days each and is therefore 6939.69 days. You will notice that this is almost the same as 19 solar years of 365.24 days, which is 6939.56 days. Presumably, you're referring to the Hebrew Calendar, a 19 year period of which consists of 12 years of 12 months plus 7 years of 13 months, thus 19 years is the period after which the Hebrew and solar calendar dates will match up."
