That hasn't been the case for me. I end up owing come tax time every year, and yet every time, after having paid what is owed, months later they give me a small refund anyways. Now I know where I can save money on my taxes, and I've done it before, but it's the savings are so small that it's not even worth the time doing. Yet, it's about what they give me in the refund. Why didn't they just keep it, especially given it's such a small amount?

How do you know the IRS is calculating it right?

Because I've gone back and done the parts of my taxes where I skipped, and low and behold the savings I would have made if I filed them, are what they gave me.

Even if they were incorrect, why did they refund me when they could of kept it?