You're assuming banks use that formula and not just YOLO it, "haha fuck you pay me more".

If you learnt calculus, you could check their work and see that it's accurate. And it only takes algebra and a few minutes of work to see that your bank statements match the formula that's been given.

▲

ErroneousBosh 12 hours ago | parent [-]

I know calculus, and I also know that mortgage payments don't follow that formula - or, maybe they do but they're so buried in noise and extra charges and costs you'd never know it.

	▲	Animats 7 hours ago \| parent [-]
		Bookkeeping normally computes interest based on some accounting period - days, weeks, months, or quarters. It's a sum of discrete charges, not an integral. It was usually monthly in the paper and pencil era; today it is usually daily. Look up "double declining balance" and "Rule of 73". Financial calculators do integrate, though. "Present value" is computed by integration.