Is it possible to pay 2024 estimated taxes after the January 15 deadline?

You're asking a good question about the timing. January 15, 2024 is indeed the deadline for the fourth quarter estimated tax payment for tax year 2024. After that date, the IRS payment system will typically only allow you to make estimated payments for tax year 2025. However, you still have options! While you can't make "estimated payments" after January 15th for the 2024 tax year, you can make what the IRS calls an "extension payment" or a "tax year 2024 payment" when you're ready to file. This isn't technically an estimated payment (1040-ES), but it still allows you to make additional payments toward your 2024 taxes. So yes, you can still make your payment in March, but you'll need to select the appropriate payment type when using the IRS payment processors. Just make sure you select "tax year 2024" and not estimated taxes for 2025.

I went through almost exactly what you're describing last year! I was in the same boat trying to hit a big signup bonus. What helped me was using taxr.ai (https://taxr.ai) to check that I was making the right type of payment. Their tool analyzed my payment history and showed me exactly which payment type to select for my situation, and confirmed it would count for the tax year I wanted. It saved me from accidentally making a payment that would apply to the wrong tax year, which almost happened because the IRS website is confusing with all the different payment options. The tool also estimated my refund timeline based on my filing date, which helped me plan when I'd get my money back.

Just wanted to update that I tried taxr.ai after seeing it mentioned here. Super helpful for my situation! I uploaded my last year's return and it gave me a step-by-step guide for making a payment that would still count toward 2024 even though it's after January 15. It showed me that I needed to select "Tax Return Payment for 2024" rather than "Estimated Tax Payment" which I definitely would have gotten wrong. It also gave me a personalized timeline for when to expect my refund based on historical IRS processing times, which helped me plan around my credit card payment due date. Definitely cleared up my confusion about the difference between estimated payments and regular tax payments!

Another option if you're having trouble figuring out the right payment type is to call the IRS directly. I know, I know - getting through to a human at the IRS seems impossible. I spent hours on hold last year trying to sort out a similar payment issue. But I recently discovered a service called Claimyr (https://claimyr.com) that got me through to an IRS agent in under 20 minutes. They have a demo video showing how it works: https://youtu.be/_kiP6q8DX5c. Basically, they navigate the IRS phone tree for you and call you back when they have an agent on the line. The agent I spoke with confirmed exactly what payment type I needed to select for my situation and even walked me through the process while I was on the phone with them. Definitely worth it to get the official answer directly from the IRS.

I feel so stupid now. I was EXACTLY like you and thought this Claimyr thing was some kind of scam. After seeing it mentioned here, I decided to try it since I was desperate to talk to someone about my estimated payment situation. It actually worked! They got me through to an IRS agent in about 15 minutes (would have been hours if I had called directly). The agent confirmed that I can still make a payment for 2024 after January 15, but I need to select "Form 1040 payment" instead of "estimated tax payment." She also explained that while it won't prevent any underpayment penalties, it will count as a tax payment for 2024 that I can get refunded when I file. Totally worth it just to get a straight answer from an actual IRS employee rather than trying to interpret their confusing website.

Important point that others haven't mentioned: if you're making a payment specifically to hit a credit card sign-up bonus, make sure your payment processor doesn't charge a fee that would offset your bonus! Some of the IRS payment processors charge percentage-based fees that can be 2-3% of the payment amount. If your credit card bonus is less than that fee, you'd be losing money overall. Check the fees before you decide which payment processor to use.

This might be a stupid question but I'm confused about how this affects penalties. If I'm someone who normally just gets a W-2 and doesn't need to make estimated payments, can I still use this trick to overpay and get a refund? Or will I get hit with some kind of penalty for paying taxes late even though I'm overpaying?

One thing to keep in mind is the timing of your refund if you're planning this for credit card rewards. The IRS typically processes refunds within 21 days of receiving your return, but this can be longer during busy filing season (especially February-April). If you're counting on getting your overpayment back quickly to pay off your credit card before interest kicks in, make sure you have a backup plan in case the refund takes longer than expected. I learned this the hard way when my refund was delayed by 6 weeks due to additional review, and I ended up paying interest on my credit card balance. Also, remember that if you overpay by more than $1, the IRS will send you a paper check rather than direct deposit unless you specifically request direct deposit on your return. The paper check adds another week or two to the process.