How Quarterly Estimated Taxes Work for Denver Freelancers and Small Business Owners
A step-by-step guide to the federal 1040-ES and Colorado DR 0104EP. Two separate systems. One hard deadline. Here's the math your quarterly payment actually requires.
A step-by-step guide to the federal 1040-ES and Colorado DR 0104EP. Two separate systems. One hard deadline. Here’s the math your quarterly payment actually requires.
Editor’s note: The Q3 estimated tax deadline follows the standard federal and Colorado schedule of September 15. The July 15 date referenced in our original pitch reflected a COVID-era extension that is no longer in effect. If you are reading this before September 15, that is your deadline. The guidance below reflects current 2025 tax-year rules. Colorado underpayment penalty rates and DR 0104EP thresholds should be confirmed against the Colorado DOR rate table and current form instructions before acting on specific figures.
The September 15 deadline doesn’t appear on most people’s radar the way April 15 does. No news segments. No tax software countdowns. No office chatter about whether you’ve filed yet.
But for Denver’s large and growing population of freelancers, independent contractors, sole proprietors, and single-member LLC owners, it’s one of the four most consequential dates on the financial calendar. Miss it, and you trigger a penalty that compounds from the day the payment was due — not from April. That distinction matters more than most first-year freelancers realize until they’re on the wrong end of it.
This piece walks through the full Q3 estimated tax obligation for a Denver freelancer: what you owe, to whom, through which portals, and calculated with real numbers. Federal and Colorado payments are completely separate systems. The math is straightforward, but you have to run it twice.
Who the September 15 Deadline Actually Hits
If you expect to owe at least $1,000 in federal income tax for the year after accounting for any withholding, the IRS expects you to pay that liability in four quarterly installments rather than one lump sum in April. Colorado works the same way: if you expect to owe Colorado income tax above the threshold in the current DR 0104EP instructions, the Colorado Department of Revenue wants quarterly payments too. Confirm the exact Colorado threshold at revenue.colorado.gov before relying on any specific figure.
The people this hits aren’t exotic edge cases. Think of the graphic designer in RiNo billing Bay Area tech companies, or the copywriter in Capitol Hill who left a salaried job in February and is now invoicing clients directly. None of these workers have an employer withholding taxes from their checks. Every dollar of tax they owe gets sent in by the taxpayer, proactively, on a schedule.
The four federal and Colorado quarterly deadlines for the 2025 tax year:
- Q1: April 15, 2025
- Q2: June 16, 2025
- Q3: September 15, 2025
- Q4: January 15, 2026
Colorado follows the same quarterly schedule as the IRS — no separate state-only deadlines to track, which is at least one thing they got right. If September 15 falls on a weekend or federal holiday, it shifts to the next business day. Check the Colorado DOR calendar each year to confirm.
Two Systems, Two Portals
Here’s where first-year freelancers stumble most often: your federal estimated tax payment and your Colorado estimated tax payment go to completely different places. Paying one does not satisfy the other. People assume otherwise and spend an anxious April figuring out why they still owe Colorado.
Federal estimated taxes route through one of two systems. IRS Direct Pay (directpay.irs.gov) requires no registration, accepts bank account payments, and is free. You select “Estimated Tax” as the payment reason and confirm the tax year. EFTPS (eftps.gov) requires enrollment but suits people making frequent payments — enrollment takes a few days for your PIN to arrive by mail, so if you haven’t set it up yet, Direct Pay is the faster option before September 15. Form 1040-ES contains a calculation worksheet and four paper vouchers if you prefer to mail a check, but the worksheet is worth reading at least once even if you pay online. It makes the structure of the calculation visible in a way that’s genuinely useful.
Colorado estimated taxes are paid separately through Revenue Online at revenue.colorado.gov. The form is DR 0104EP. If you prefer to mail a check, make it payable to the Colorado Department of Revenue, include the paper DR 0104EP voucher, and write your Social Security number or ITIN on the memo line. Mailed payments must be postmarked by the deadline, not received by it. With September 15 this close, paying through Revenue Online eliminates any postmark ambiguity — who wants to be betting on USPS processing times for a tax payment? Verify the current mailing address on the DR 0104EP instructions before sending anything by mail.
The Math — What You Actually Owe This Quarter
A concrete example: a Denver freelance UX designer expecting $80,000 in net profit for 2025 after legitimate business deductions — software subscriptions, professional development, home office. No W-2 income, no withholding. Here’s her Q3 math.
Step 1: Self-Employment Tax (Federal)
Self-employed workers pay both the employee and employer halves of Social Security and Medicare. This is the part that consistently surprises people who’ve only ever had a salary — your employer was quietly covering half of that bill the entire time you worked for them. The calculation starts with net profit:
$80,000 × 0.9235 = $73,880 (self-employment earnings, using the 92.35% multiplier that accounts for the employer-side contribution not being subject to self-employment tax itself)
$73,880 × 0.153 = $11,304 (total self-employment tax for the year)
Step 2: Federal Income Tax
Before calculating federal income tax, she deducts half of the self-employment tax:
$11,304 ÷ 2 = $5,652 (above-the-line deduction)
$80,000 − $5,652 = $74,348 (adjusted income for federal tax purposes)
From this figure, subtract the 2025 standard deduction — it adjusts annually for inflation, so verify the current figure against IRS guidance. For a single filer at this income level, federal taxable income lands in the mid-to-upper $50,000 range after the standard deduction. That income falls across the 10%, 12%, and 22% brackets. Rather than cite specific bracket thresholds here, work through the calculation using the IRS tax tables for 2025. At this income level, estimated federal income tax runs roughly $8,000 to $9,000 before credits — run the current-year tables for your actual number.
Total federal tax obligation for the year: self-employment tax ($11,304) plus the federal income tax from the bracket calculation. Divide by four for the quarterly payment. For this designer, the Q3 federal payment lands somewhere in the $4,800–$5,300 range. Use the 1040-ES worksheet with current figures rather than relying on this illustration.
Step 3: Colorado Income Tax
Colorado’s flat income tax rate is 4.4% for the 2025 tax year. The Colorado calculation uses net profit after allowable Colorado modifications — for most freelancers, that’s close to the same number used for federal purposes. Colorado taxable income here is approximately $74,348. At 4.4%, that’s roughly $3,271 in Colorado income tax for the year, or about $818 per quarter.
So for Q3, this designer owes roughly $818 to the Colorado DOR and a separate federal payment calculated from the 1040-ES worksheet. Two payments. Two portals. No coordination between them — the IRS and the Colorado DOR do not speak to each other about your account. It’s a cumbersome system, but it’s the one we have.
One more thing worth saying plainly: these are estimates, and that’s the entire point. If your income fluctuates quarter to quarter — and for most Denver freelancers it does — recalculate before each payment rather than dividing a January projection by four and repeating it blindly. A bad quarter doesn’t mean you’re locked into overpaying the next three.
The Safe Harbor Rule — How to Know You’ve Paid Enough
“Safe harbor” is tax jargon for a floor. Pay at least the safe harbor amount each quarter and you’re protected from underpayment penalties even if your final April bill turns out higher than expected. You’ll still owe the difference in April — safe harbor doesn’t reduce your tax bill, it just eliminates the quarterly penalty. Think of it as a defense against the penalty clock, not against the tax itself.
For federal estimated taxes, two safe harbor thresholds exist. The simpler path: pay 100% of your prior-year tax liability across four equal installments. If your total federal tax bill in 2024 was $16,000, paying $4,000 per quarter in 2025 protects you from penalties regardless of what you actually end up owing. There’s a catch for higher earners. If your adjusted gross income in the prior year exceeded $150,000, safe harbor requires 110% of your prior-year liability — not 100%. This matters for higher-earning Denver freelancers and consultants, the kind billing $200 an hour to multiple tech clients who wonder why their quarterly math keeps coming up short. If your 2024 AGI was $160,000, you need 110% of your 2024 liability spread across four quarters. The alternative: pay 90% of your current year’s actual tax liability using real-time income data, which requires accurate projections but works well when income has grown significantly.
Colorado’s safe harbor rule is simpler: pay 100% of your prior-year Colorado tax liability across four equal installments. As of the current DR 0104EP instructions, Colorado does not have a 110% tier for high earners. The 90% current-year rule applies at the state level as well.
A practical approach many Denver freelancers use: find the total tax line on last year’s Colorado return, divide by four, and pay that as a baseline. Track whether current-year income is running meaningfully higher. If it is, bump the payment up. Not glamorous, but it works and it’s defensible.
What Happens If You Miss the Deadline
Missing a quarterly payment isn’t a criminal matter and doesn’t trigger an audit by itself. It’s a civil, interest-based penalty calculated on the amount you underpaid for that specific quarter. The clock starts on the due date — not when you eventually get around to paying.
Federal underpayment penalty: The IRS calculates this using the federal short-term rate plus 3 percentage points, compounded daily. The exact rate fluctuates quarterly. Verify the current rate in the Form 2210 instructions or at irs.gov before calculating what you owe. The penalty runs from the missed due date until you pay, or until April 15, whichever comes first. Form 2210 is where you calculate and report it if your underpayment extends beyond a single quarter or if you want to claim relief under the annualized income installment method.
Colorado underpayment penalty: Colorado uses the same structure — federal short-term rate plus 3% — which also fluctuates quarterly. Verify the current Colorado rate at revenue.colorado.gov. Each quarter is assessed independently. An overpayment in Q4 does not retroactively cancel a Q3 shortfall. The penalty clock on Q3 starts September 15 and runs until the tax is paid or the annual return due date. The Colorado underpayment calculation form is in the DOR forms library at revenue.colorado.gov — verify the current form number there, since form numbers update periodically.
If you missed Q2 or earlier and haven’t paid, pay now. Every day extends the penalty period. The amount you’ll owe in penalties for a missed quarter is real but manageable if you act quickly. Carrying the full underpayment through April will cost significantly more.
I Just Started Freelancing This Year — Do I Owe Q3?
If you began earning freelance or self-employment income for the first time in Q3, you’re not required to have made Q1 or Q2 estimated payments. You had no self-employment income in those periods. The IRS allows you to use the annualized income installment method (Form 2210, Schedule AI) to calculate each quarter’s required payment based only on income actually earned that quarter, rather than spreading an annual estimate evenly across all four. Colorado offers a parallel provision. This method protects first-year freelancers from penalties on quarters when they had no self-employment income.
What this does not mean: you can’t skip all estimated payments and settle up in April penalty-free. If you expect to owe more than $1,000 in federal tax for the full year, you should begin making estimated payments in Q3 now. Check the current DR 0104EP instructions for the Colorado threshold. The lump-sum bill in April will be larger, and you may owe penalty on Q3 and Q4 underpayment depending on your total liability.
First-year freelancers commonly conflate the estimated payment with the annual return. They’re different processes. The estimated payment is a prepayment of tax owed on current-year income, due September 15. The annual return (federal Form 1040, Colorado Form DR 0104) is filed and reconciled the following spring. Your estimated payments reduce what you owe on the annual return — or they create a refund if you’ve overpaid.
If you left a W-2 job mid-year, your former employer’s withholding covers the period you were employed. Your estimated tax obligation starts from the first quarter in which you had meaningful self-employment income. Calculate accordingly.
Edge Cases Worth Knowing
S-Corp Owner-Employees
If you’ve elected S-corp status for your Denver LLC, you likely pay yourself a W-2 salary through payroll, which has withholding attached. Beyond that salary, the distributive share of S-corp profits passes through to your personal return and is subject to income tax, though not self-employment tax. That’s a key advantage of the S-corp structure — one reason plenty of Denver consultants making north of $80,000 net go through the S-corp election process. The estimated tax obligation applies to that distributive share. Many S-corp owners adjust their own payroll withholding to cover it rather than making separate quarterly estimated payments. Mechanically simpler if you can tune the withholding correctly, but the underlying obligation is the same either way.
Side Gig Income Added to a Salaried Job
If you have a full-time W-2 job and earn additional freelance income on the side, the $1,000 federal threshold applies to your total expected tax owed after withholding — not just the side income. Your employer’s withholding may cover most of your base salary tax, but if your side income generates enough additional liability, you may cross $1,000 on that income alone. Even modest freelance income — say, $8,000 in photography work — can trigger an estimated tax obligation if your effective rate on that income (including self-employment tax) pushes the bill past the threshold. A lot of people assume their W-2 withholding covers everything, then wonder why April felt expensive.
Denver Freelancers with Out-of-State Clients
A significant portion of Denver’s freelance workforce bills clients in California, New York, and Texas — especially in tech, media, and consulting — and this creates recurring anxiety about multi-state tax exposure. The short answer: you don’t owe California or New York income tax simply because your client is based there. Colorado taxes all income earned by Colorado residents regardless of where the client is located. You owe Colorado tax at 4.4% on your net income from all sources. The only scenario that changes this is if you have a permanent place of business or meet a nexus threshold in another state — that situation warrants a CPA conversation, but it doesn’t apply to the typical remote Denver freelancer billing out-of-state clients from their kitchen table.
Denver-Specific Details That Don’t Affect Your Quarterly Payment (But Come Up Every Time)
Two Denver-specific obligations create confusion because freelancers often encounter them at the same moment they’re dealing with estimated tax questions — usually right after forming an LLC or landing their first big contract, when everything hits at once. Both are entirely separate from quarterly estimated income tax.
Denver Occupational Privilege Tax (OPT): Denver levies an Occupational Privilege Tax of $5.75 per month on the employee side, plus $4.00 per month on the employer side if you have employees. For a solo freelancer with no employees, the self-employed version applies at $5.75 monthly. Flat tax, not income-based, filed through the Denver Department of Finance. It doesn’t appear on DR 0104EP and has no interaction with the 4.4% state rate. Separate process, separate portal, separate payment.
LLC Registration and Business Licenses: Many Denver freelancers who’ve recently registered an LLC with the Colorado Secretary of State (sos.colorado.gov) or obtained a Denver Business License through the Excise and Licenses portal (denvergov.org/exciseandbillings) find these administrative steps prompt a flurry of tax questions all at once. Legitimate steps for running a legitimate business, but they don’t change your estimated tax calculation. Your tax obligation flows from your income, not from whether you have an LLC. Keep those two things separate and the paperwork becomes a lot less overwhelming. For a fuller look at how much it actually costs to form an LLC in Colorado, including state filing fees and ongoing compliance costs, see our breakdown for Denver small-business owners.
Resources and Where to Go From Here
For a Denver freelancer acting before September 15, here are the specific tools:
Colorado estimated tax payment: Revenue Online at revenue.colorado.gov. Download the current DR 0104EP form and instructions from the same site.
Federal estimated tax payment: IRS Direct Pay at directpay.irs.gov. Free. Immediate. No enrollment required. Select “Estimated Tax,” tax year 2025.
Federal underpayment worksheet: Form 2210 and its instructions at irs.gov.
Colorado underpayment calculation: Available through the Colorado DOR forms library at revenue.colorado.gov. Verify the current form number on that page.
Local CPA referrals: The Colorado Society of CPAs maintains a Find-a-CPA directory at cocpa.org, useful for finding a Denver-area CPA or Enrolled Agent who regularly works with self-employed clients.
A Denver-area CPA who reviews self-employed returns regularly can help you reconstruct your actual income and deductions for the year so far. That’s far more useful than estimating blindly. If you’re carrying real uncertainty about whether your projections are accurate, a one-hour consultation before September 15 is worth more than several hours of spreadsheet anxiety after it. This kind of guidance is exactly what you’ll find covered throughout our business and professional coverage for Denver freelancers and small-business owners.
The next two dates every new Denver freelancer should put on the calendar:
September 15, 2025 — Q3 federal and Colorado estimated tax deadline
January 15, 2026 — Q4 federal and Colorado estimated tax deadline
After January 15, the annual returns are due in April, where your estimated payments are applied against your final liability. Get the quarterly payments right and April is a reconciliation. Get them wrong and it’s a bill with interest attached. The math isn’t complicated. It just has to get done.
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