Hello. Im returning to work after a brief vacation (I work a school schedule) recently I consolidated my personal debt into a loan through my credit union. It's a 5 year loan and without many details, obviously paying the minimum will have it settled on 5 years. However, my hours aren't constant and I do get overtime which I intend to put towards the loan. For my neurotic self, I like to calculate how much time it'll take me to pay off paying a certain amount each month and their are calculators for that. However. Since some months I'll pay the minimum, and other months a payment might be double the minimum or even 1000 dollars, I'd like to calculate how much that changes the time frame to paying off what I owe. Does anyone know the formula for calculating debt and apr? This'll be a fun if not complicated way of keeping me busy and helping me keep myself focused on my goal.