First, if your friend has capital gains, as the person who previously responded mentioned, then there should be a schedule in the return which shows the calculation.
If he does not have capital gains, the only thing that I can think of for this year was if your friend did not receive one of the stimulus checks (say the $600. one) he would be getting it as a credit on the return thereby lowering the tax.
If neither of those is applicable, carefully go over the return again, make sure all the elections and questions are answered correctly, and make sure all the balances are correct.
Without seeing the return, it's hard to figure what else is causing the difference.
Good Luck.
