How do I calculate a simple year/month/day subtraction?

Let me first explain this problem... in Indian Vedic astrology a person undergoes a period of a planet say, Saturn, 19 years. Let us say a 5 years 5 months and 20 days have passed in to that period. I have to get a remainder of 13 years 7 months and 10 days.

How could I get excel to do this simple subtraction with out it giving me dates like 1900 and so one?

Please indicate the date format I should use in the cells...

Thanks.

Thanks & Best Regards Priyantha A Dias