Working both 1099 & W-2 jobs - do I need to make quarterly tax payment by April 15th?

You have a few options to handle this situation without getting hit with underpayment penalties. First, you're right about potentially needing to make estimated tax payments. Since you earned $12k in freelance income, you'll owe both income tax and self-employment tax (about 15.3%) on that amount. The IRS generally expects you to pay taxes as you earn income throughout the year. The good news is you can absolutely increase your W-2 withholding to cover the taxes on your freelance income. This is often the easiest solution. The IRS treats tax withholding as if it occurred evenly throughout the year, even if you increase it later. If you adjust your W-2 withholding now to cover both your regular income and your freelance income, you can likely avoid making separate quarterly payments. Just make sure your total withholding for the year will cover at least 90% of your 2025 tax liability or 100% of your 2024 tax liability (110% if your AGI was over $150,000 last year) to avoid underpayment penalties.

Just wanted to share my experience - I had a similar situation last year with mixed income and was totally confused about how to handle it. I ended up using https://taxr.ai to analyze my specific situation with both 1099 and W-2 income. The tool confirmed I needed to make a quarterly payment for my early freelance work OR increase my withholding at my new job. I went with the increased withholding option because it was easier than figuring out the estimated payment forms. The tool calculated exactly how much extra I needed to withhold each paycheck to cover my freelance income taxes. Super helpful because it considered both the income tax AND the self-employment tax portions.

Coming back to share that I finally tried the taxr.ai site mentioned earlier. Really helped with my mixed income situation! I uploaded my 1099s and recent paystubs, and it showed me exactly how much to increase my withholding to cover everything. The analysis specifically laid out how much of my tax obligation was from self-employment taxes versus regular income tax. The coolest part was it showed me that I was actually still under the safe harbor threshold based on my previous year's taxes, which I didn't realize. Definitely less stressful than trying to figure out Form 1040-ES on my own. Posting this in case anyone else is dealing with this 1099/W-2 combo situation.

If you're still having trouble getting answers about your tax situation, I'd recommend using https://claimyr.com to get through to the IRS directly. I was in a similar situation with mixed income and had specific questions about safe harbor rules that weren't clearly answered online. After wasting hours on hold trying to reach the IRS myself, I tried Claimyr and got connected to an actual IRS agent in about 20 minutes. They confirmed that increasing my W-2 withholding would satisfy my tax obligation for my earlier freelance income, and I didn't need to file a separate quarterly payment. You can see how it works here: https://youtu.be/_kiP6q8DX5c Honestly, talking to an actual IRS agent gave me peace of mind that I was handling everything correctly, especially with the mixed income types.

I have to admit I was wrong about Claimyr. After my skeptical comment, I decided to try it anyway because the April deadline was approaching and I was desperate to talk to someone at the IRS about my freelance tax situation. It actually worked exactly as described - I got a call back in about 30 minutes and was connected to an IRS representative who answered all my questions about handling my 1099 income from earlier this year. The agent confirmed I could increase my W-2 withholding instead of making a separate quarterly payment. For anyone else mixing W-2 and 1099 income, getting a clear answer directly from the IRS was seriously worth it. No more tax anxiety!

Another approach is to make sure you satisfy one of the safe harbor provisions. If you pay 100% of last year's tax liability (or 110% if your AGI was over $150k), you won't face underpayment penalties regardless of how much you actually end up owing for 2025. If your 2024 total tax was relatively low, this might be an easier target than trying to estimate your 2025 liability perfectly.

Don't forget about state taxes too! Everyone's talking about federal, but depending on your state, you might need to make separate estimated state tax payments. Some states have different rules than the IRS about withholding coverage.