Does anyone have a way of estimating repayments? The typical situation is $1,000,000 over a 25 year period with monthly payments at interest rates which vary between 2% and 5%. Like to vary the period too, anywhere from 20 to 40 years. Not expecting any degree of real accuracy, approximate values are ok.

I think Excel even has a template for that kind of stuff.

That works too depending on your needs; however, if you have different rates for different periods, youâ€™ll have to resort to a spreadsheetâ€¦ or at least itâ€™ll be a more convenient alternative. Such online calculators are convenient though when itâ€™s just one simple interest rate.

As far as back-of-the-envolop-ing a 25 year period with varying rates or even scenarios of varying periodsâ€¦ Iâ€™d strongly discourage you from doing so, because even people that should know (MBA, CFA, etc.) how to do it will save themselves the embarrassment of potentially being way off just because of compounding and quickly whip up a spreadsheet instead.

Also, certain places you can make additional lump sum payments each year, with or without a fee and then Excel and especially its scenario tools come in handy. Of course, if you know what youâ€™re doing, you can use the crystal ball add in or even do goal-seeking in Excel to find you the best option.

Thanks all for your responses. I usually use Excel to calculate projections but had hoped to find a mental math approximation. The key I suppose is to memorise some numbers which is ok and look for associated patterns (if any exist) when you vary interest rate or term. Facilitating this exercise is that interest rates have remained steady.