I went about it the long way. The mortgage data sits alongside all of my other metrics (bank balances, health stats, car stats, utilities etc).
So there’s a row per date, with calculations for interest accrued for that date etc. Its definitely not the smartest or fastest way to do it, but it keeps everything in line and comparable. So I can see what impact each mortgage payment makes on the interest per day for example.
I try to keep all of my key metrics in one sheet to allow me to do comparisons across categories. For example I can compare miles driven versus electricity use per day, or number of steps versus bank balance, or the amount of solar exported versus interest accrued (they’re not all useful comparisons haha).
Another screenshot showing the impact of overpayments;
