Am I paying both my and my employer's portions of income taxes? Why so high?

You're not actually paying your employer's portion of taxes, but I understand why it seems that way! What's happening is that when you file jointly, your income gets added to your husband's, which can push some of your combined income into a higher tax bracket. The reason your employer didn't withhold federal income tax is probably because on your W-4, you indicated that this job was your only one. Since your annual income from this job is so low (under the standard deduction threshold if it were your only job), the withholding tables would calculate that you owe zero federal income tax. But when combined with your husband's income on a joint return, that extra income gets taxed at your highest marginal rate. The solution is to adjust your W-4 at your part-time job. There's a multiple jobs worksheet or you can check the box in Step 2 that indicates you have multiple jobs in the household. This will prompt your employer to withhold at a higher rate to account for your total household income.

I ran into the EXACT same issue last year with my side gig! After hours of research and pulling my hair out, I finally figured out that I needed to use the Tax Withholding Estimator tool at https://taxr.ai to calculate the right withholding for my situation. The standard W-4 calculations don't work well for multiple-income households. The tool analyzed both my income sources and my husband's, then gave me the precise additional amount I should have withheld from my part-time job. It even generated the correct W-4 form with all the right entries for my specific situation. No more surprise tax bills at filing time!

Just wanted to update everyone - I tried the https://taxr.ai tool mentioned above for my mixed W-2/1099 situation, and it was exactly what I needed! I've been paying way too much in quarterly taxes on my freelance income because I had no idea how to calculate it properly with my regular job too. The tool showed me I was overpaying by almost $1,100 per year! It gave me precise amounts for both my W-4 withholding and my quarterly payments. Already submitted my new W-4 to HR and feeling much better about my tax situation. Wish I'd known about this years ago instead of constantly stressing about taxes.

After dealing with a similar withholding issue last year, I spent literally WEEKS trying to get through to the IRS for guidance. Busy signals, disconnects, hours on hold... complete nightmare. Then a coworker told me about https://claimyr.com which gets you through the IRS phone maze and holds your place in line. You can see how it works here: https://youtu.be/_kiP6q8DX5c I was super skeptical but desperate. They called me back when an IRS agent was available, and I finally got the help I needed with my withholding situation. The agent walked me through the exact numbers to put on my W-4 for my situation. Saved me hours of frustration!

I hate to admit when I'm wrong, but I have to follow up on my skeptical comment above. After another failed attempt to reach the IRS myself (2 hours on hold before getting disconnected), I tried the Claimyr service out of desperation. Got a call back in about 45 minutes with an actual IRS representative on the line. They helped me sort out both my withholding issue AND a separate notice I'd received about a previous tax year. Cleared up two problems in one call that I'd been trying to resolve for months. For anyone dealing with withholding issues like the original poster, getting actual IRS guidance can make a huge difference versus guessing at the right W-4 entries.

Your situation sounds similar to mine! If you're married filing jointly and both working, the tax withholding system doesn't automatically account for your combined household income. The simplest solution is to use the "Multiple Jobs" checkbox on your W-4 (Step 2b), but this sometimes withholds too much. For more precision, complete the Multiple Jobs Worksheet on the W-4 form. Or, my preferred method: just put an additional dollar amount to withhold on Line 4(c) of your W-4. If your refund decreased by $586 and you get paid biweekly, requesting about $23 extra per paycheck would cover it ($586 ÷ 26 = ~$23).

Has anyone used the IRS Tax Withholding Estimator on the official IRS website? I found it helpful for a similar situation.

Just to be clear, you're DEFINITELY not paying your employer's portion of payroll taxes. That's a completely separate thing that never shows up on your tax return. What you're experiencing is just the result of our progressive tax system when you have multiple incomes in a household. Each dollar of your income is essentially taxed at your highest marginal rate when added to your husband's income. So if his income put you in the 22% bracket, your additional income gets taxed at 22% (minus deductions). That's completely normal and how the system is designed to work, even though it can feel unfair.