You'll get a letter from them on why here pretty soon. You're math was either way off. You don't qualify for certain credits. Or you owe money for something like child support, student loans, or unpaid taxes from previous years.
Are you expecting both Federal and state refunds? If so, are you sure it's not the state refund? The Fed and state refunds come in separate deposits.
Look at your actual Federal return and verify the amount shown on your Federal Form 1040, Line 21a.
Are there any messages when you check the IRS "Where's My Refund" tool, such as if there has been an offset?
https://www.irs.gov/Refunds
If the IRS reduced your refund, you should get a letter in about 3 weeks or so explaining why, or you can phone them. We can tell you how to reach a live IRS agent.
How did you pay your TurboTax fees? Did you pay your TurboTax fees upfront, or did you choose to pay the fees out of the Federal refund? I ask because if you chose to pay the fees out of the Federal refund, an intermediary bank is involved in the process, and you may be able to log in to the intermediary company for refund info.