How Much to Set Aside for Small Business Taxes

Running a small business is already a constant juggle of cash flow, suppliers, and customers—tax surprises shouldn’t be another bowling pin in the air. The good news: with a simple framework and a few Beancount tricks, you can translate “I hope the tax bill isn’t huge” into a predictable monthly transfer.

1. Know What You’re Really Paying For

Before you can set money aside, you need to know where it’s going. For most U.S. small businesses (especially sole proprietorships and partnerships), the total tax liability is a combination of several distinct obligations.

• Federal Income Tax: This is a progressive tax, meaning the rate increases as your income does. For 2025, brackets go up to $37,%$ for single incomes above $626,350 and married-filing-jointly (MFJ) incomes above $751,600.
• Self-Employment (SE) Tax: This is the entrepreneur's version of FICA taxes (Social Security and Medicare) that W-2 employees pay. It’s a flat $15.3,%$ on your first chunk of net earnings. The $12.4,%$ Social Security portion stops once your profit hits the annual wage base, which is projected to be $176,100 in 2025. The remaining $2.9,%$ for Medicare continues on all profits.
• State & Local Income Tax: This varies wildly by location, ranging from $0,%$ in states like Wyoming and Texas to over $13,%$ in California's top bracket.
• Quarterly Underpayment Penalties: The IRS wants its money throughout the year, not all at once. To avoid penalties, you generally must pre-pay at least $90,%$ of your current year's tax liability or $100,%$ of your previous year's tax bill (this threshold rises to $110,%$ if your adjusted gross income, or AGI, is over $150,000).

Quick heuristic: Most U.S. solopreneurs who live in an average-tax state end up owing $25,% - 30,%$ of net profit once federal, SE, and state taxes are combined.

2. A Three-Step Estimate You Can Update Monthly

You don’t need complex software to get a handle on this. A simple, repeatable process is all it takes.

1. Project Annual Profit: Look at your year-to-date performance and make a reasonable forecast for the full year. The basic formula is your friend: Projected Revenue - Projected Deductible Expenses = Projected Profit.
2. Apply an Effective Tax Rate: Start with a reasonable percentage. If you have last year’s tax return, you can calculate your effective rate from that. If you're new to this, the $30,%$ heuristic is a safe starting point.
3. Divide by 12 (or 52): Take your total estimated annual tax and divide it by the number of pay periods you want to use. We recommend monthly. Move that amount into a dedicated tax-reserve bank account every month. If your cash flow is more volatile, a weekly transfer might feel more manageable.

3. Implement It in Beancount

Plain-text accounting makes this process transparent and auditable. Here’s how to manage your tax savings in Beancount.

First, create a routine transaction to move your monthly savings from your primary checking account to a separate, dedicated savings account for taxes.

; Reserve July's taxes
2025-07-31 * "Tax reserve transfer"
  Assets:Bank:Checking          -3000 USD
  Assets:Bank:TaxReserve         3000 USD
  Equity:Opening-Balances

When you make a quarterly estimated payment to the government, you record the actual liability. The payment comes directly from your reserve account.

; Record liability when you file the quarterly payment
2025-09-15 * "Q3 estimated tax payment"
  Assets:Bank:TaxReserve        -9000 USD
  Liabilities:Taxes:Federal      6000 USD
  Liabilities:Taxes:State        3000 USD

This simple system buys you three powerful advantages:

• Immediate Visibility: Your Assets:Bank:TaxReserve balance always shows what’s already “spoken for.” You know at a glance that this cash isn't available for other business expenses.
• Accurate Profit: Because the reserve is treated as a transfer between asset accounts, your Profit & Loss statement isn’t distorted. You only record the tax liability when you actually file and pay it.
• Audit Trail: Every payment to the IRS or your state treasury ties back to a clearly tagged movement from your reserve account, creating a clean paper trail.

4. Fine-Tuning Your Percentage

The initial $25,% - 30,%$ estimate is a great start, but you should adjust it based on your specific business model.

• High-Margin Consultants / Agencies: If you clear well above the Social Security wage base ($176,100), your effective tax rate will climb. A rate of $30,% - 35,%$ is likely more accurate.
• Product Businesses with Heavy Deductions: If you have significant costs of goods sold (COGS), inventory, or other deductions, your net profit margin is lower. A rate of $20,% - 25,%$ may suffice. Use Form 1040-ES worksheets each quarter to confirm.
• S-Corp Owners: Your situation is different. The "reasonable salary" you pay yourself is subject to standard payroll withholding (FICA and income taxes). Your distributions (profits paid out beyond salary) still require quarterly estimated payments, but often at a lower marginal rate since they aren't subject to SE tax.
• Multi-State Sellers: If you have "nexus" (a significant business presence) in multiple states, you may owe income tax in each. This can stack your liabilities. For clarity, create separate liability accounts in Beancount, such as Liabilities:Taxes:State:CA and Liabilities:Taxes:State:NY.

5. Automate, Review, Repeat

A system only works if you use it. Make it effortless.

• Automate: Link your main operating account to a high-yield savings account named something like "TaxReserve." Schedule an automatic transfer to occur right after you close your books each month.
• Review: Re-forecast your annual profit quarterly. If Q2 sales blew past expectations, increase your monthly reserve amount immediately. Don't wait until January to discover you've under-saved.
• Repeat: Keep key documents organized within your Beancount directory. Saving last year’s final tax return (document: "2024/Taxes/Form1040.pdf") gives you one-click context when discussing numbers with your CPA or planning for the next year.

Closing Thoughts

Tax bills feel random only when the set-aside process is. By baking a percentage-based reserve directly into your double-entry accounting flow, you trade anxiety for algebra—and Beancount makes the math (and the audit trail) trivial. Review your rate each quarter, keep Assets:Bank:TaxReserve funded, and April 15th turns back into just another day of business as usual.

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Disclaimer: This article is for educational purposes only and isn’t tax advice. Always confirm numbers with a qualified professional for your jurisdiction and entity type.