How to check the numbers in an AI answer

Find the number the decision rests on

Set the working aside and find the figure you would act on: the saving, the payment, the deadline, the amount due. That is the one to recompute. In our loan examples, the figure that came out wrong was usually the one the question asked for.

Check the period of every rate

An annual rate used as a monthly one, or a nominal rate treated as an effective one, changes every number after it. “10% a year” can mean 0.833% a month (nominal) or about 0.797% (effective); a careful answer says which it used.

Example check: Extra $300 a month on a $400k mortgage: an AI's maths, checked

Count dates the way the rule does

Many rules count both the first and the last day. Counted that way, January 10 to March 20 is 70 days; subtracting the dates gives 69. One day can be the difference between a legal stay and an overstay.

Example check: Back to Europe after 70 days? The 90/180 rule, checked

Use a tool, not a reread

A spreadsheet's PMT function, a bank's or a government's calculator, or the official tool for the rule (such as the EU's short-stay calculator) settles in seconds what rereading won't.