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A standard for transparent math

Math Shouldn't Be
a Black Box.

Every calculator on this platform shows exactly how it got its answer — the formula, your numbers, and the logic. Always.

Try a ShowMath Calculator →

Why we built this

Calculators online give you a number.
They never explain why.

You put numbers in, a number comes out. You have no idea if it's right, outdated, or using your state's actual rules. You can't verify it. You can't learn from it. You just have to trust it.

When it's your taxes, your retirement, your freelance rate — that's not good enough. The difference between a correct and incorrect quarterly estimate can mean a penalty, an audit flag, or leaving thousands on the table.

So we built calculators that show their work. Every step. Every formula. Every IRS citation. That's ShowMath.

How it works

Every step. Every formula. Every source.

Here's a live ShowMath panel — the actual component used on every calculator. Click “Show the math” to expand it.

Self-Employment Tax — $80,000 grossLive demo
1

Gross income

Your total self-employment income before any deductions

= $80,000

This is everything you earned as a freelancer or independent contractor before expenses or taxes.

2

Net earnings adjustment

Gross Income × 0.9235

$80,000 × 0.9235

= $73,880

The IRS reduces your SE income by 7.65% before calculating SE tax. This mirrors the employer-equivalent FICA portion that W-2 workers never pay tax on.

IRS Schedule SE (Form 1040), Line 4a

3

Self-employment tax

SE Base × 15.3% (12.4% SS + 2.9% Medicare)

$73,880 × 0.153

= $11,304

15.3% covers both Social Security (12.4%, capped at $168,600) and Medicare (2.9%, uncapped). Self-employed pay both the employee and employer halves.

IRS Publication 334, Chapter 4; IRC §1401(a)(b)

4

SE tax deduction

SE Tax ÷ 2

$11,304 ÷ 2

= $5,652

You deduct the employer-equivalent half of SE tax above-the-line. This reduces your AGI before income tax is calculated.

IRS Form 1040, Schedule 1, Line 15; IRC §164(f)

5

Adjusted gross income

Gross Income − ½ SE Deduction

$80,000 − $5,652

= $74,348

AGI is the foundation for your federal income tax calculation.

6

Taxable income

AGI − Standard Deduction

$74,348 − $14,600

= $59,748

2024 standard deduction for single filers is $14,600.

IRS Revenue Procedure 2023-34

7

Federal income tax

2024 marginal brackets applied to taxable income

$11,600 × 10% + $35,550 × 12% + $12,598 × 22%

= $8,198

Each dollar is taxed only at its bracket rate. Your top bracket (22%) only applies to income above $47,150.

IRS Revenue Procedure 2023-34, Table 1

8

Total tax burden

SE Tax + Federal Income Tax

$11,304 + $8,198

= $19,501

9

Effective total tax rate

Total Tax ÷ Gross Income × 100

$19,501 ÷ $80,000 × 100

= 24.4%

Your effective rate combines SE tax and federal income tax. It’s always lower than your marginal bracket because of progressive brackets and deductions.

10

Take-home after all taxes

Gross Income − Total Tax

$80,000 − $19,501

= $60,499

What lands in your pocket after self-employment tax and federal income tax. State tax not included.

Key insight

On $80,000 gross: SE tax is $11,304, federal income tax is $8,198, total tax is $19,501 (24.4% effective rate). Take-home: $60,499.

#ShowYourWork

The standard

ShowMath isn't just a feature. It's a standard.

Every calculator on this site is built to this standard: real math, real sources, real answers.

🔍

Transparent

You see every step, not just the answer. The formula comes first, then your numbers, then the result. Nothing is hidden.

📜

Cited

Formulas reference IRS publications, financial standards, and real math. If we used it, we cite it. You can verify every number.

🔓

Free

No paywalls on the math. Ever. No premium tier to unlock the formula. The work is the product — always.

Powered by ShowMath

Free tools for freelancers

Every tool below shows its full math. Pick one and see for yourself.

W-2 vs 1099 Calculator

ShowMath

Same gross pay, wildly different take-home. See exactly how W-2 and 1099 offers compare after self-employment tax, FICA, and employer benefits — then get the break-even number that tells you exactly what to negotiate.

Show the math →

Freelance Rate Calculator

ShowMath

What should you actually charge per hour? Account for taxes, health insurance, retirement, and the hours you can't bill — get the real number.

Show the math →

Tax Bracket Visualizer 2024

ShowMath

Visual, educational tool showing exactly how 2024 federal tax brackets work. Stacked bar chart for each bracket, effective vs marginal rate, pre-tax deductions, and the bracket bump myth — busted with the math shown.

Show the math →

Compound Interest Calculator

ShowMath

See how your money grows with compound interest and regular contributions. Watch year-by-year growth, apply the Rule of 72, and see the real power of compounding.

Show the math →

Self-Employment Tax Calculator

ShowMath

Calculate your exact self-employment tax using the IRS formula. Shows SE tax (SS + Medicare), the half-SE deduction, 2024 federal income tax brackets, effective rate, take-home pay, and quarterly estimated payment.

Show the math →

1099 Quarterly Tax Planner

ShowMath

Calculate your quarterly IRS payments with QBI deduction (Section 199A), safe harbor, and all 4 due dates. Adds the 20% pass-through deduction that most freelancers forget to claim.

Show the math →

See all tools →
🧮

Try it yourself — Self-Employment Tax

The most impactful calculator for any 1099 worker. Enter your gross income and see the full SE tax math — including the §164(f) deduction most people miss.

Open SE Tax Calculator →
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