I agree talk with an accountant there are deductions to be had you may need to file an amended return.
ARCOgraphite said:Beyond that as also noted, you can start paying quarterly estimated taxes. Really if you've been writing that big a check at tax time, you should have started the quarterly estimated tax payments. If you haven't been hit with a penalty to this point, pretty lucky I'd think. Anything over a grand owed, unless you had withholding increased, starting quarterly estimated taxes at same time a good strategy ime.
And if there is a penalty owed the IRS will figure it for you and send you the bill. There's been years I thought I might get one, but didn't. However, I always started estimated tax payments with the check for due taxes.
As per my understanding, the IRS GENERALLY doesn't start assessing underpayment penalties unless you end up owing more than ~10% of your total tax liability when filing your taxes. I've also read(but don't take this as gospel) that they're upping it to ~15% for the 2018 tax year as there was some uncertainty in the first couple of months of the year while they were working out the details of the tax reform.
In any case, my income MOSTLY comes from two sources-the majority of it is from my regular full-time job, but I have some self employment/contract income that I do on the side and usually amounts to 10-15% of the amount of my full time salary. I started that business toward the end of a tax year, so initially just made a single estimated payment to account for the taxes on that money(self employment can hit you hard since it's an extra ~15% for social security and medicare on top of the income tax). Just so that I have one less thing to keep track of, I have extra witholding on both the federal and state taken out of my main paycheck in lieu of paying estimated taxes on the small business(although admittedly sometimes income from that is sporadic and in big chunks, so in that case I'll just send in an estimated based on my best guess at profits as soon as the money is in). Both of those strategies have worked for me, and I usually end up on the side of getting a smallish refund on the federal(a few hundred dollars).
As far as estimated vs. payroll with-holding to pay for income outside your job-it's been explained to me that the IRS doesn't really care HOW you pay your taxes-they just care about getting them and getting them on time.