Hi, Tom.
There's no way that we can guess what your next year's tax might be. There are SO MANY variables! First, of course, is the amountS of your income. Yes, that's a capital S because there are multiple amountS of income involved. How much income do you have that IS subject to withholding? How much do you have that is NOT? Of that not-subject income, how much is self-employment income and thus subject to the self-employment tax? And, of course, your expected deductions will affect the amount of your taxes, too, both income tax and SE tax.
I've been away from the subject for over 10 years and I'm sure a lot of the estimated tax rules have changed. In the olden days, there were many exceptions to the requirement that at least 90% of the tax (both income and SE tax) be prepaid - and that the quarterly estimates be adequate, as well as the annual total. ONE of the exceptions that we relied on most often was that there would be no penalty if the next year's estimate was at least as much as the prior year's tax. But remember, that means having as much as last year's tax paid in, including both withholding and estimated payments. In other words, even if next year's tax is exactly the same as this year's, your estimated tax payments would need to be more if your withholding is expected to be less.
TurboTax doesn't just make up the numbers. It gets them by calculating from the information YOU fed in. What did YOU tell TurboTax about YOUR expectations for next year? About your expected salary, your expected self-employment income, your expected deductions...?
RC