Forum Moderators: phranque
if so, you can do a pretty trivial spreadsheet showing a column with various payments in each row, then in the next column calculate a % increase. your next month's estimated value would then be the last month's value times (1 + the average % increase for the past, say, three months).
if you have a lot of past history, you can get much more complex to accommodate seasonal variation, if any, etc.