In the most basic case of a term loan, with a repayment Monthly as per repayment start date, annuities differ from what every other loan calculator I checked would come up with.

Also, the last annuity is slightly lower than all the other ones:

Reason turns out to be that annuities are – always – automatically rounded to the next full currency unit – in this case from 3,226.25 to 3,227.00. Thus, in the end, slightly less than a full annuity remains open.

I can see that for some currencies, subunits are so small they may or may not be considered at all. But this needs to be some kind of optional “Round up“ feature rather than being built into the original formula.

For comparison, here are two calculators and some full repayment schedules:

• https://www.calculator.net/loan-calculator.html?cloanamount=100%2C000&cloanterm=3&cloantermmonth=0&cinterestrate=9.99&ccompound=monthly&cpayback=month&x=Calculate&type=1#amortized-result

• Kreditrechner.pdf / https://www.zinsen-berechnen.de/kreditrechner.php?paramid=4rm4k6zne8

• Frappe Lending.pdf