How many exemptions/allowances should I put on my W-4?

Single and 1 or maybe 2. MFS is the WORST way to file.

At the end of 2018, you will NOT claim your son as a dependent. The dependent exemption is eliminated with the 2018 tax law. To make up for the loss of dependent exemptions, the standard deduction was increased and the child tax credit was doubled.

That said, you can claim as many allowances on the W-4 as you choose.

Because you want to file MFS, more of your income will be subject to the 22% bracket than if you were MFJ.

Your estimated income of $81k will be reduced to $69k by the $12k standard deduction. Assuming you and your spouse split the child tax credit down the middle, that $1,000 that is your share will come off of your tax bill.

You will owe 10% on the first $9,525 of that $69k. $953

12% on the next $29,175 $3,501

22% on the final $30,300 $6,666

Total $11,120

- $1,000 child tax credit $10,120

That will be your approximate tax bill for 2018.

Look at your last pay stub for each job. Add up the total. If the total is about 50% and you expect to earn about the same money for the rest of the year, then you don't need to change anything on the W-4. If your tax withholding is more than half, you can change the W-4 to take one more allowance, and cut the tax withheld. And the opposite if your tax withheld is less than 50% of the estimated total for the year - claim one less allowance. Or, in my case, I would leave it as is and write a check in 2019. Coming out even is the goal, but when I'm off, I'd rather pay than get a refund. I like getting all of my money during the year and making Uncle Sam wait a bit to get the rest of his. It's an interest-free loan to me, instead of the exact opposite, what a tax refund is.

You should IGNORE every 'rule of thumb' you get here.

The BEST answer is to get your hands on a 2018 tax form, and complete it using the numbers you expect for the end of the year. Then use withholding tables to find what comes closest to withholding your actual tax liability.

As that is rarely feasible, the next best is to use the withholding calculator on the IRS website to make a similar estimate.

One on the W-4 for the full time job and zero on the W-4 for the part time job.

You should claim 2 on the main job, and 0 on the side job.

Dependents are irrelevant under the GOP tax code.

>"I want to have LESS taken out of my paycheck but not have to owe anything at the end of the year."

It doesn't work like that. You owe some amount. If you don't pay it now, you will pay it later.

It is almost always better for a married couple to file jointly. If you don't trust your spouse enough to sign your name on his/her financial assertions, then the ability to file as Single is just one reason you need a divorce.

The IRS website has a withholding calculator. It will give you a suggestion.

How old is your son? Is he a full time student? How much income will he have for the year? How many allowances did you claim for the FIRST half of the year?

You can file whatever you want and even change it later but I'd just claim 1 exemption for now (and you'll likely still owe money when tax time comes around). You could easily claim 2 exemptions instead but for your situation I suspect you are going to owe. If you want you can see how much is taken out with 1 exemption, figure out that number for the entire year and then back of the envelope kinda figure out what your tax owed will be and then see how the numbers compare and adjust the exemptions accordingly.