Did you try it with a period greater than 12 months ? It works for me.
That's the point of the +12*(YEAR(B1)-YEAR(A1)) part of the formula ... it
adds 12 for each change of year.


"happywitchie" wrote in message
ups.com...
Thanks for this.

It works a treat if I'm looking at a 12 month period. But it won't work
for a period greater than that - unless maybe I have done something
wrong....

Thanks for the base logic - I'll try playing around with it some more.