Calculating difference between two dates

I know about the normal formula to calculate the difference between two dates (=(YEAR(A4)-YEAR(A3))*12+MONTH(A4)-MONTH(A3)), however, I'd like a formula that does the same thing but doesn't round up, ie it takes into account the days, and reports back only full months between the two dates.

For example if a child was born on the 26th May 2009, and today is the 25th May 2010, they are not yet 12 months old (1year), they are 11 months old.

Does anyone know the correct formula for this?

Thanks

aha, DATEDIF, that's what I was looking for - thank you!!!

I'll try and put it into practise but may need to ask a question about that if I dn't get it quite right.

As expected I have a couple of queries on how to apply it.

I'm calculating what age a parent was, when their child was born, so if the child's age is in A2, and the parent in B2, the formula would be
=DATEDIF(A2,B2,"m") ? that gives me a #NUM! error
or
=DATEDIF(D23,E23,m) ? that gives me a #NAME? error

I know I'm doing something obvious wrong!

Sorry, they are dates - in the format DD/MM/YYYY

Aha, knew it would be something silly!

Thanks a lot.

I think I've asked this before a few months back but the forum has no record of that thread.