I posted this once today already, but I can't find my original question
anywhere!

I need a formula which will enter a loan payment on the same date each month
over a 30-year period. I have a long spreadsheet which calculates the
interest on a daily compound basis, using one row for each day. This needs
to take into account months with 28/30/31 days, and also leap years.

Any help will be much appreciated!