Doing your own taxes really isn’t like changing your own oil.

Even if you enjoy such tasks, getting either one of them wrong as a do-it-yourselfer can be expensive. But as complicated as a car engine may be for a relative novice, an encounter with the tax code offers so many more costly ways for things to go spectacularly awry.

This tax season, consider the danger of human error: namely, your own.

Here are nine situations that may persuade you to turn the task over to a pro.

1. Small errors lead to expensive tax bills.

Tax software — or the old-fashioned paper forms and calculators — won’t help much when the numbers that human beings use in the first place are flawed.

Finding and entering tax information often isn’t always easy. “That part of the process requires reading comprehension and critical thinking skills, made more complicated by a specialized vocabulary,” said Lynn Henley, an accountant in Pacifica, Calif.