# Q4 Side Hustle Tax Deadlines to Know Before December

> Side hustle income has two tax deadlines before April: September 15 and January 15. Here's what each one covers and how to avoid a penalty.

Canonical: https://smartcentsclub.com/articles/q4-side-hustle-tax-deadlines-you-ll-miss-if-you-wait-until-d/
Published: 2026-10-02

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You started your side hustle to bring in extra money, not to become your own payroll department. So when tax season only lives in your head as "sometime in April," it is an easy assumption to make. The problem is that side hustle income does not work on the same calendar as a paycheck, and the IRS has already set deadlines for the rest of this year that have nothing to do with April.

In the back half of the year, there are two dates on that calendar that matter, and neither one waits for you to feel ready. If your side hustle picked up this year, whether it's freelance work, resale, tutoring, or gig platform driving, this is the part of the year worth pausing on before it slips past you.

> **The short answer:** if your side hustle brings in income with no taxes withheld, the IRS expects payments four times a year, not once. For the 2026 tax year, the third one was due September 15, 2026, and the last one lands January 15, 2027, both before your regular spring filing deadline ([IRS.gov](https://www.irs.gov/faqs/estimated-tax), accessed 2026-09-07; [IRS Form 1040-ES](https://www.irs.gov/pub/irs-pdf/f1040es.pdf)).

## Why This Catches Side Hustlers Off Guard

Your budget didn't fail because you're bad with money, and this isn't about being disorganized either. It's about a mismatch between how your side income arrives and how the tax system is built to collect on it.

When you work a regular job, your employer takes a bite out of every paycheck and sends it to the IRS for you. You barely notice it happening. Side hustle income, gig work, freelance invoices, resale profits, generally skips that step entirely. Nobody withholds anything before the money lands in your account, which is exactly why quarterly payments exist as the standard requirement instead of a single April filing ([IRS.gov](https://www.irs.gov/businesses/small-businesses-self-employed/manage-taxes-for-your-gig-work)).

So the pattern is simple: a paycheck job trains you to think of taxes as something that happens automatically in the background. A side hustle removes that automation, and the IRS still expects the same result, just on a schedule you now have to track yourself.

That habit is stubborn because it isn't really about taxes at all. It's about which parts of your financial life run on autopilot and which ones need you to show up and do the work by hand. A side hustle quietly moves one more thing from the "autopilot" column into the "you have to remember this" column, and calendars are notoriously bad at flagging that shift on their own.

## The Four Payment Periods, In Plain Terms

The IRS divides the year into four estimated tax periods, and each one has its own due date. Here is the full schedule, straight from the source:

- January 1 through March 31, due April 15
- April 1 through May 31, due June 15
- June 1 through August 31, due September 15
- September 1 through December 31, due January 15 of the following year

That breakdown comes directly from the IRS "Estimated tax" FAQ ([IRS.gov](https://www.irs.gov/faqs/estimated-tax), accessed 2026-09-07). Notice that the periods are not even quarters of equal length. The third period is three months, but the fourth stretches over four, from September through December, which is exactly the window most side hustlers are in right now.

For this tax year specifically, that means the third payment is due September 15, 2026, and the fourth is due January 15, 2027 ([IRS Form 1040-ES](https://www.irs.gov/pub/irs-pdf/f1040es.pdf), 2026).

## What September 15 and January 15 Actually Mean for You

If you're reading this in early fall, the September 15 date has just passed. It covers income you earned from June through August. If you missed it, don't panic and don't try to just fold it into your next payment. Pay it as soon as you can, since the penalty is figured on each underpayment for the number of days it remains unpaid ([IRS Form 1040-ES](https://www.irs.gov/pub/irs-pdf/f1040es.pdf)).

The January 15 deadline is the one people forget entirely, because it falls right after the holidays and feels like it belongs to "next year's taxes." It doesn't. It covers income from September through December of this year, and it's still due before you file your annual return in the spring. That's the trap in the article title: if you wait until December to think about taxes, you'll walk straight past this deadline without noticing, and it comes back around again every year for anyone earning income the IRS doesn't already withhold on your behalf ([IRS.gov](https://www.irs.gov/faqs/estimated-tax), accessed 2026-09-07).

If your side income overlaps with 1099 work, it helps to understand how that income is taxed differently from a W-2 paycheck in the first place. This comparison walks through what actually changes: [1099 vs W-2 Side Income: What Changes on Your Taxes](/articles/1099-vs-w-2-side-income-what-actually-changes-on-your-tax/).

## Do You Even Have to Pay Quarterly?

Not everyone with a side hustle needs to make these payments. The general rule from the IRS is that you generally need to make estimated payments if you expect to owe at least $1,000 in tax for the year after subtracting whatever is already withheld and any refundable credits you qualify for ($1,000 threshold, [IRS.gov](https://www.irs.gov/faqs/estimated-tax), accessed 2026-09-07). The IRS adds a second test: your withholding and credits also have to fall short of the smaller of 90% of this year's tax or 100% of last year's tax (110% if last year's adjusted gross income was over $150,000).

In plain terms: if your side hustle is small and your day job's withholding already covers what you'd owe, you may not need to send in separate quarterly payments at all. If your side income is a meaningful chunk of your household budget, or it's your only income, that $1,000 threshold is easy to cross without realizing it.

This is genuinely worth sitting down and checking rather than guessing. Your results will vary depending on your household's full tax picture, deductions, and filing status, so this isn't something a blanket rule can answer for you.

## How Much to Set Aside, Without Guessing

There is no single percentage to set aside that fits everyone, and honestly, anyone who tells you a flat number without knowing your income, deductions, and filing status is guessing too. What's worth doing instead is treating the question as ongoing rather than a one-time answer.

A few habits make this less stressful regardless of the exact number:

- Base what you set aside on actual profit, meaning income after your side hustle expenses, not the full amount that lands in your account.
- Keep it in a separate account so it isn't sitting in your everyday spending money, quietly getting spent before September or January arrives.
- Revisit the amount each quarter instead of setting it once in January and forgetting about it, since a busy summer side hustle can look very different from a slow winter one.

None of that replaces sitting down with your actual numbers or a tax professional who can look at your full picture. It just keeps the deadline from arriving as a surprise.

## The One Way to Skip the January Payment

There's a lesser-known exception built into the rules, and it's worth knowing about even if you don't end up using it. If you file your complete 2026 tax return and pay the entire balance due by February 1, 2027, you can skip the January 15, 2027 estimated payment entirely (the "January payment" exception, [IRS Form 1040-ES](https://www.irs.gov/pub/irs-pdf/f1040es.pdf)).

That's a narrow window: full return, full payment, by February 1, 2027. For most side hustlers, that's a tight turnaround right after the holidays, especially if you're still gathering 1099 forms or receipts. If you'd rather not race that clock, making the January 15 estimated payment on time is the more realistic path for most people. If you want a head start on gathering what you'll need before those forms even arrive, this walks through the prep: [1099 Season Prep: What Side Hustlers Need to Know](/articles/1099-season-prep-what-side-hustlers-need-before-january-31/).

## What Happens If You Miss a Deadline

Here's the part that surprises people most: underpayment penalties can apply even if you're going to get a refund when you actually file your return in the spring ([IRS.gov](https://www.irs.gov/faqs/estimated-tax)). Owing money at the end of the year and owing a penalty for late quarterly payments are two separate things. You can technically be "even" with the IRS by April and still have picked up a penalty for how you paid along the way.

This is exactly the misconception worth naming out loud: thinking "I only deal with taxes once a year in April" works fine if you have a regular paycheck with automatic withholding. It does not work the same way for income that arrives with nothing withheld, which is most side hustle and gig income. The system is built around quarterly check-ins, not one annual reckoning.

It also helps to remember why the penalty exists in the first place. The IRS built the quarterly system so tax gets paid roughly as income is earned, similar to how withholding works for an employee. When a payment period passes with nothing sent in, that's treated as a gap in the pay-as-you-go schedule, separate from whatever your final bill looks like at filing time. Two different questions, two different outcomes, even though they both involve the same tax year.

## How to Handle This Without Overthinking It

Here is the math, and here is the one thing to do this week. You don't need a full tax strategy session to get ahead of this. You need to know two things: whether you're over that $1,000 threshold, and which of the two fall deadlines applies to you right now, a missed September 15 payment or January 15.

If September 15 has already passed and you haven't made that payment, the one small next action is to figure out what you owe for that period and send it in now rather than waiting for January. If you're squarely in the September through December window, the one small next action is simpler: put the January 15, 2027 date somewhere you'll actually see it in December, not buried in an app you only open in April.

That's it. Not a full overhaul of how you handle money, not a new system, just one date and one number, so the holidays don't quietly swallow a deadline that's easy to forget and comes with a real cost if you miss it.

## Your Next Step

Pull up your side hustle income for the year so far and compare it against that $1,000 estimated tax threshold. If you're close to or over it, make sure the September 15 payment is covered and mark January 15, 2027 somewhere you'll see it before the holidays hit, since a missed quarterly payment can carry a penalty even when you're owed a refund at filing time. None of this replaces a conversation with a tax professional about your specific situation, but knowing which deadline applies to you is the first step toward not being caught off guard by it.