Freelancer Retirement Calculator in Google Sheets: SEP IRA vs Solo 401k (2026)
Self-employed workers have access to some of the most powerful retirement accounts in the entire tax code — yet most freelancers contribute nothing, or far less than they're legally allowed. In 2026, a freelancer earning $100,000 can shelter up to $37,500 from taxes using a SEP IRA, or up to $54,500 using a Solo 401(k). This guide shows you how to build a free retirement calculator in Google Sheets that computes your maximum contribution, compares both account types, and projects your balance in 10, 20, and 30 years.
Table of Contents
- Why Retirement Accounts Are the Ultimate Freelancer Tax Tool
- SEP IRA vs Solo 401(k): Core Differences
- 2026 Contribution Limits: What You Can Actually Put In
- The 4-Tab Google Sheets Calculator Structure
- Tab 1: Your Numbers (Inputs)
- Tab 2: SEP IRA Calculator
- Tab 3: Solo 401(k) Calculator
- Tab 4: 30-Year Growth Projections
- Key Formulas to Copy-Paste
- Worked Example: $80K Net Income Freelancer
- Which Account Is Right for You?
- 5 Costly Retirement Mistakes Freelancers Make
Why Retirement Accounts Are the Ultimate Freelancer Tax Tool
For W-2 employees, retirement contributions reduce their taxable income. For freelancers, it does that plus it reduces their self-employment tax base. That's a double benefit most employees don't have.
Here's the mechanism: contributions to a SEP IRA or pre-tax Solo 401(k) reduce your adjusted gross income (AGI). Lower AGI means lower income taxes. But for freelancers, it also affects the income used to calculate quarterly estimated payments, the 3.8% net investment income surtax threshold, and various other phase-outs.
Example: A freelancer earning $120,000 who contributes $36,000 to a Solo 401(k) reduces their federal taxable income to $84,000. At a 22% marginal rate, that's a $7,920 tax reduction. Add state income taxes and the number climbs further. The money doesn't disappear — it grows tax-deferred in the retirement account and is taxed at (presumably lower) rates in retirement.
The compound effect: $30,000 contributed at age 35 becomes approximately $161,000 at age 65 assuming 6% annual returns. The same $30,000 paid in taxes generates $0. Every dollar you don't shelter is a permanent loss, not a deferral.
SEP IRA vs Solo 401(k): Core Differences
Both accounts are designed for self-employed individuals and small business owners. Both allow large tax-deductible contributions. The differences matter depending on your income level, age, and how much administrative complexity you're willing to tolerate.
| Feature | SEP IRA | Solo 401(k) |
|---|---|---|
| Who can open | Any self-employed person | Self-employed with no full-time employees (except spouse) |
| 2026 contribution limit | $72,000 (or 25% of comp) | $72,000 + $8,000 catch-up (age 50+) |
| Employee deferral component | No | Yes — up to $24,500 (2026) |
| Contribution at low income | Lower (employer-only formula) | Higher (employee deferral available) |
| Roth option | No (pre-tax only) | Yes (Roth Solo 401k available) |
| Loans allowed | No | Yes (up to 50% of balance, $50K max) |
| Admin complexity | Very simple (no annual filing) | Moderate (Form 5500-EZ if balance >$250K) |
| Setup deadline | Tax filing deadline (including extension) | December 31 of tax year |
| Best for | Simplicity; incomes above $150K where both max out | Most freelancers — especially those earning $50K–$150K |
Solo 401(k) has a hard deadline: You must establish the Solo 401(k) by December 31 of the tax year you want to make contributions for. A SEP IRA can be opened and funded as late as your tax filing deadline (plus extension). If you're reading this in December, act now on Solo 401(k) or you'll lose 2026.
2026 Contribution Limits: What You Can Actually Put In
The IRS sets these limits annually. For 2026, both accounts share the same $72,000 total limit — but how you get there is very different.
SEP IRA: The Simple Formula
SEP IRA contributions are employer contributions only. The formula is 25% of net self-employment compensation — but for a sole proprietor, "net compensation" is your net profit adjusted for the SE tax deduction.
The actual effective rate is approximately 20% of net self-employment income (after subtracting half of SE tax), not 25% of gross profit. This confuses many freelancers who expect to contribute 25% of their revenue.
Solo 401(k): Two Buckets
The Solo 401(k) has an employee deferral component (up to $24,500 in 2026) plus an employer contribution component (up to 25% of W-2 wages, or ~20% of net SE income for sole proprietors). The total of both cannot exceed $72,000.
This two-bucket structure means a freelancer earning $80,000 can contribute far more to a Solo 401(k) than a SEP IRA at that income level:
| Net SE Income | SEP IRA Max | Solo 401(k) Max (Under 50) | Solo 401(k) Max (Age 50+) |
|---|---|---|---|
| $40,000 | $7,294 | $29,796 | $37,796 |
| $60,000 | $11,068 | $35,570 | $43,570 |
| $80,000 | $14,842 | $39,344 | $47,344 |
| $100,000 | $18,587 | $43,089 | $51,089 |
| $150,000 | $27,962 | $52,464 | $60,464 |
| $250,000+ | $72,000 | $72,000 | $80,000 |
The higher your income, the closer the two accounts converge. At $250,000+ net SE income, both cap at $72,000. Below that, Solo 401(k) consistently wins on maximum contribution — often by $15,000–$25,000 per year.
The 4-Tab Google Sheets Calculator Structure
| Tab | Name | What It Does |
|---|---|---|
| 1 | Inputs | Your income, age, filing status, existing balances |
| 2 | SEP IRA | Maximum contribution formula, tax savings calculation |
| 3 | Solo 401(k) | Employee deferral + employer contribution, comparison vs SEP |
| 4 | Projections | 30-year balance projections at multiple contribution levels and return rates |
Tab 1: Your Numbers (Inputs)
This tab feeds all other calculations. Every other tab pulls from here using cell references — change one number and everything updates.
| Field | Cell | Notes |
|---|---|---|
| Tax Year | B1 | 2026 |
| Age | B2 | Your current age (affects catch-up contribution eligibility) |
| Net Self-Employment Profit | B3 | Gross revenue minus business expenses, before retirement contribution |
| Other W-2 Income | B4 | Include if you have a day job in addition to freelance |
| Filing Status | B5 | Single / MFJ / MFS / HoH (dropdown) |
| Federal Tax Bracket | B6 | Marginal rate: 10%, 12%, 22%, 24%, 32%, 35%, 37% |
| State Tax Rate | B7 | Your state's income tax rate (0% if no state income tax) |
| Existing Retirement Balance | B8 | Current balance in any retirement accounts |
| Expected Annual Return | B9 | Conservative default: 6% (adjust to your risk profile) |
| Years Until Retirement | B10 | =65-B2 or manual entry |
Tab 2: SEP IRA Calculator
The SEP IRA tab walks through the exact IRS formula step by step, so you know you're not over-contributing (a common and penalizable mistake).
The IRS SEP IRA Calculation Steps
- Start with net self-employment profit (Schedule C, Line 31)
- Multiply by 92.35% to get net SE earnings (deducting half of SE tax)
- Calculate SE tax: net SE earnings × 15.3%
- SE tax deduction: SE tax ÷ 2
- Net SE compensation: Profit − SE tax deduction
- SEP IRA max contribution: min(net SE comp × 25%, $72,000)
- But effective rate on gross profit is ~20%, not 25%
Net_SE_Earnings = B3 * 0.9235
SE_Tax = Net_SE_Earnings * 0.153
SE_Tax_Deduction = SE_Tax / 2
Net_SE_Compensation = B3 - SE_Tax_Deduction
SEP_Max = MIN(Net_SE_Compensation * 0.25, 72000)
Tax Savings Calculation
Federal_Savings = SEP_Contribution * Inputs!B6
State_Savings = SEP_Contribution * Inputs!B7
SE_Tax_Savings = 0 (SEP doesn't reduce SE tax base directly)
Total_Savings = Federal_Savings + State_Savings
Tab 3: Solo 401(k) Calculator
The Solo 401(k) tab splits the calculation into two buckets and shows the combined maximum — plus the delta vs. SEP IRA, so you can see exactly how much extra you could be sheltering.
Employee_Deferral_Limit = 24500
Catch_Up = IF(Inputs!B2 >= 50, 8000, 0)
Max_Employee_Deferral = MIN(Net_SE_Earnings, Employee_Deferral_Limit + Catch_Up)
Net_SE_Compensation = B3 - SE_Tax_Deduction (same as SEP tab)
Employer_Contribution = MIN(Net_SE_Compensation * 0.25, 72000 - Employee_Deferral)
Solo401k_Max = MIN(Employee_Deferral + Employer_Contribution, 72000 + Catch_Up)
Extra_vs_SEP = Solo401k_Max - SEP_Max
Tab 4: 30-Year Growth Projections
This tab converts abstract contribution limits into real money. It shows your projected retirement balance at 10, 20, and 30 years under three scenarios: contributing nothing, contributing the SEP IRA maximum, and contributing the Solo 401(k) maximum.
=FV(rate, nper, pmt, pv)
= FV(Inputs!B9, Inputs!B10, -Annual_Contribution, -Inputs!B8)
Example Projection Table: $80,000 Net SE Income, Age 40, 6% Returns
| Scenario | Annual Contribution | Balance at 10 Years | Balance at 20 Years | Balance at 25 Years |
|---|---|---|---|---|
| No contributions | $0 | $0 | $0 | $0 |
| SEP IRA max | $14,842 | $195,892 | $546,040 | $817,439 |
| Solo 401(k) max | $39,344 | $519,548 | $1,447,963 | $2,168,139 |
| Solo 401(k) 50% of max | $19,672 | $259,774 | $723,982 | $1,084,070 |
The difference between SEP IRA maximum and Solo 401(k) maximum at $80K income is $24,502/year in contributions. Over 25 years at 6% returns, that gap compounds to $1.35 million in additional retirement balance. That's the cost of using the simpler account when you don't have to.
Key Formulas to Copy-Paste
Complete SEP IRA Max in One Formula
=MIN((B3-(B3*0.9235*0.153/2))*0.25, 72000)
Solo 401(k) Employee Deferral Available
=MIN(B3*0.9235, 24500 + IF(B2>=50, 8000, 0))
Future Value with Annual Contributions
=FV(B9, B10, -Annual_Contribution, -B8)
Tax Savings from Contribution
=Contribution * (Federal_Rate + State_Rate)
Worked Example: $80K Net Income Freelancer
Let's walk through a real example. Sarah is a freelance UX designer, 38 years old, single filer, with $80,000 in net SE income after business expenses. She's in the 22% federal bracket and pays 5% state income tax.
| Step | Calculation | Result |
|---|---|---|
| Net SE earnings (92.35%) | $80,000 × 0.9235 | $73,880 |
| SE tax (15.3%) | $73,880 × 0.153 | $11,304 |
| SE tax deduction (½) | $11,304 ÷ 2 | $5,652 |
| Net SE compensation | $80,000 − $5,652 | $74,348 |
| SEP IRA Maximum | $74,348 × 25% | $18,587 |
| Solo 401k employer portion | $74,348 × 25% | $18,587 |
| Solo 401k employee deferral | min($73,880, $24,500) | $24,500 |
| Solo 401(k) Maximum | $18,587 + $24,500 | $43,087 |
| Extra deferral vs SEP IRA | $43,087 − $18,587 | +$24,500 |
| Total tax saved (Solo 401k, 27%) | $43,087 × 27% | $11,633 saved |
Sarah saves $11,633 in taxes by maxing a Solo 401(k) versus $5,018 with a SEP IRA — a difference of $6,615 more in Sarah's pocket this year, while also sheltering $24,500 more for retirement.
Which Account Is Right for You?
Choose SEP IRA if:
- Your income is above $200,000 and both accounts approach the same limit anyway
- You want zero admin complexity — SEP IRA requires no annual filing, ever
- You're starting late in the year and missed the Solo 401(k) December 31 setup deadline
- You might hire employees in the next year (Solo 401(k) disqualifies when you have full-time employees)
- You prefer to open and contribute as late as your tax deadline (including extensions)
Choose Solo 401(k) if:
- Your income is below $200,000 (the contribution advantage is significant)
- You want to maximize tax deferral and you're under 50
- You want a catch-up contribution option (age 50+)
- You want the option of Roth contributions (not available in SEP IRA)
- You want the ability to take a loan from the account if needed
- You're self-employed with no plans to hire full-time employees
The practical answer for most freelancers: If you earn under $200,000 and you have no employees, open a Solo 401(k) by December 31. The contribution advantage compounds into a massive difference over a career. The admin complexity is manageable — Form 5500-EZ is only required once your balance exceeds $250,000, and it's a one-page form.
5 Costly Retirement Mistakes Freelancers Make
1. Using 25% of Revenue Instead of Net Compensation
The SEP IRA limit is 25% of net self-employment compensation, not 25% of gross revenue. After expenses, SE tax deduction, and the adjustment factors, the real effective rate on net profit is approximately 20%. Over-contributing triggers a 6% excise tax per year until corrected — an avoidable and expensive error.
2. Waiting Until High Income to Start
A Solo 401(k) at $40,000 income still lets you defer up to ~$29,796. The tax savings may seem small, but the compound growth on early contributions is enormous. A $20,000 contribution at 35 grows to $114,870 at 65 at 6% — before any additional contributions. Time is the scarcest resource in retirement planning.
3. Missing the Solo 401(k) Setup Deadline
Unlike a SEP IRA, a Solo 401(k) must be established by December 31 of the year you want to contribute for. It can be funded by your tax filing deadline, but the plan must exist before year-end. Missing this deadline costs you a full year of higher contribution limits.
4. Not Tracking Contributions Against Your Financial Dashboard
Retirement contributions are one of your largest annual financial decisions. They should be tracked alongside your income, expenses, and tax estimates — not siloed in a brokerage portal. Your Google Sheets financial dashboard should include a retirement contribution line so you can see the full picture each month.
5. Treating Retirement Contributions as Optional in Slow Months
For freelancers with variable income, retirement contributions need a systematic approach — not "I'll contribute when it's a good month." Consider the "save first" approach: transfer 15–20% of every client payment directly to your retirement account before anything else. What's left is your operating budget. This eliminates decision fatigue and builds the habit regardless of monthly variation.
Track Your Finances Like a Business
The Freelancer Financial Dashboard from SheetStackStudio gives you a complete income, expense, and tax tracker in Google Sheets — built to adapt for retirement contribution tracking alongside your day-to-day finances. Instant download.
Get the Template on Etsy — $12.99 →Build It Once, Use It Every Year
The retirement calculator you build in Google Sheets will serve you for your entire freelance career. Update the Inputs tab each January with your new income projection, current account balance, and updated contribution limits (the IRS adjusts them for inflation). In 30 minutes once a year, you'll know exactly what to contribute, which account beats the other at your income level, and what your retirement balance will look like in 10, 20, and 30 years.
That's information most freelancers don't have — and it's the kind of clarity that turns a tax burden into a retirement strategy.