Q3 Estimated Taxes Are Due September 15: A Two-Hour Prep Checklist

Most self-employed people handle quarterly estimated taxes the same way. Sometime around the 13th, a vague dread sets in. On the 14th, they open their bank account, look at a number, feel bad about it, and send whatever they sent last quarter. Then they close the laptop and try not to think about it again for three months.

It does not need to take three months of low-grade worry and one bad evening. It takes about two hours, once, if you do it in the right order.

The federal deadline is Tuesday, September 15. Indiana's is the same day.

The quarters are not quarters. This trips up almost everyone.

Q1 covers January through March. Q2 covers April and May, just two months. Q3 covers June, July, and August, and it is due September 15. Q4 covers September through December and is not due until January 15.

So the payment you are making this month is for summer income. If you had a slow June and a huge August, that matters. If you have been paying the same amount every quarter regardless of what you actually earned, that is worth a look, because the calculation is supposed to track the income as it comes in.

Block out one afternoon. Put the phone somewhere else.

Open your bookkeeping software and reconcile every business account against the bank statement through the end of August. Business checking, business savings, any business credit card, and any payment processor holding a balance.

This is the load-bearing step. Everything that follows is only as good as this. If your accounts are not reconciled, you are not calculating an estimate, you are guessing with extra steps.

If you are months behind and this block turns into a wall, stop. Trying to reconstruct half a year the night before a deadline is how people end up filing something they know is wrong. Make a reasonable payment based on last year, then fix the underlying problem properly.

Every transaction should be categorized. The uncategorized bucket is where deductions go to die, and everything sitting in it is money you may not get credit for.

While you are in there, chase the missing receipts. Annual renewals, anything bought through an app store, and any charge over a few hundred dollars are the ones worth having documentation for.

Bank deposits are not the same thing as your income, and the difference is where mistakes hide.

Check that everything is captured: direct deposits, payment processors, marketplace platforms, and anything paid by check that you might have deposited without invoicing. Then check the other direction and make sure things that are not income have not been counted as income. Transfers between your own accounts, a personal contribution to the business, and a loan or credit line are not revenue, and each of them inflates the number if miscategorized.

If you took large client deposits this summer for work you have not delivered yet, note it. On cash basis books that money is generally taxable when received, which is a real cash flow issue if you have already spent it against a project you have not finished.

There are two honest roads here, and the right one depends on your situation.

The safe harbor road. Federal and Indiana rules both provide safe harbors that protect you from underpayment penalties. Generally, paying 100% of last year's total tax liability does it, or 110% if your adjusted gross income was above $150,000. Take last year's total tax, apply the right percentage, divide by four, and that is your quarterly payment. It is predictable, it is defensible, and it is the low-stress option for anyone whose income is roughly similar year over year.

The catch: if this year is much bigger than last year, safe harbor keeps you penalty-free but leaves you with a large balance due in April. You avoid the penalty and inherit a cash flow problem.

The actual income road. Take your year-to-date net profit from the books you just cleaned up, project the rest of the year, and estimate the tax on that. This tracks reality better and prevents April surprises, but it requires reasonable assumptions and it takes longer.

Two things people forget when they do this themselves. Self-employment tax is generally the larger piece for most freelancers, not income tax, so an estimate built only on income tax brackets will be well short. And a mid-year income spike may allow for a different calculation method, which is exactly the kind of thing worth asking a tax professional about rather than guessing.

We are bookkeepers, not tax preparers. Our job is making sure the numbers you build this on are right. Which percentage applies to you is a question for whoever prepares your return.

Two payments, not one. This is the step Indiana residents most often get half right.

Federal goes to the IRS, which you can do through IRS Direct Pay or EFTPS. Take the confirmation number.

Indiana goes to the Department of Revenue, and you can pay through INTIME without creating an account, or mail Form ES-40. The threshold for being required to pay is $1,000 or more in combined state and county tax for the year that withholding does not cover.

That word "combined" is the part people miss. Indiana has a flat state rate, and on top of it all 92 counties levy their own income tax, based on where you lived or worked at the start of the year. Neither number alone might cross the threshold while the two together clearly do. If you have been paying federal estimates faithfully and ignoring the state side, this is worth fixing now rather than in April.

Two things left, and the first one is where we see the most common bookkeeping error of the entire quarter.

Your estimated tax payment is not a business expense. For a sole proprietor or single-member LLC, personal income tax paid from the business account is an owner's draw, not a deductible cost of doing business. Categorizing it as an expense understates your profit, which quietly corrupts every number you look at for the rest of the year, including the ones you use to calculate the next estimate. Set up a draw or distribution account and put it there.

Then set up Q4 so this is easier in January. Move money into a separate tax savings account as each client payment clears rather than at the end of the month, and put January 15 on the calendar with a reminder a week ahead.

Pay it as soon as you can rather than rolling it into September. Underpayment penalties are generally calculated per period, so an April shortfall keeps accruing until it is paid, and waiting does not make it cheaper.

If you are employed somewhere in addition to freelancing, or your spouse is, adjusting withholding on the job is sometimes a cleaner fix than writing quarterly checks, because withholding is generally treated as paid evenly across the year regardless of when it happened. That is a conversation to have with your tax preparer before December.

The two-hour version only works if the books are current. Everything in the first hour is bookkeeping, not tax work, and the reason quarterly estimates feel awful is almost never the arithmetic. It is that the underlying records are a mess, so every quarter starts with three weeks of dread and ends with a guess.

Clients whose books are reconciled monthly do not have a September 15 problem. They have a September 15 task, which takes about twenty minutes, because the first hour of this checklist was already done in August.

We are Allen & Guthrie, Hunter and Jordan, two people who handle bookkeeping for independent professionals and small service businesses. Every client works directly with one of us, and nothing gets outsourced.

We keep books reconciled and current so that quarterly deadlines are routine instead of stressful, and we take on cleanup work for people who have fallen behind. You can see what we do and what it costs on our site, because you should not have to sit through a sales call to find out our pricing.

If this September was harder than it should have been, book a free 30-minute call. Bring your last bank statement. We will tell you honestly where things stand and what it would take to make January boring.

Book your free 30-minute call

Allen & Guthrie provides bookkeeping services and does not provide tax or legal advice. Estimated tax requirements, safe harbor percentages, and penalties depend on your entity type and circumstances, and rules change. Confirm the details with a qualified tax professional, and verify current deadlines and thresholds with the IRS and the Indiana Department of Revenue.