The Busy Owner's DIY Tax Planning Guide

Why reactive filing costs you

Most profitable business owners pay more in taxes than they should — not because their CPA makes mistakes, but because the conversation happens in March instead of October. By the time you’re signing your return, the planning window has closed.

Reactive filing means you’re writing checks instead of making decisions. Proactive planning means you understand what you owe before you owe it, and you have time to do something about it.

This guide covers the three levers that matter most for a profitable service business: your S-corp salary, your quarterly estimates, and the coordination between your business and personal returns.

Getting your S-corp salary right

What “reasonable compensation” actually means

If you’re operating as an S-corp, you’re required to pay yourself a “reasonable” W-2 salary before taking distributions. The IRS defines reasonable as what you’d pay someone else to do your job. That standard is intentionally vague — and that’s where planning lives.

Set your salary too low and you risk an IRS audit that reclassifies distributions as wages — triggering back payroll taxes, penalties, and interest. Set it too high and you’re over-paying FICA and self-employment tax unnecessarily.

The right salary is defensible, documented, and calibrated to your role — not a round number someone picked years ago.

What sets your salary range

• BLS wage data for your role and industry — the IRS uses this as a benchmark
• Hours you work in the business and your specific duties
• Gross revenue of the business (higher revenue supports a higher salary)
• Whether you’re the sole owner-operator or one of several working owners
• Comparable salaries in your market for similar roles

Quarterly estimates that aren't guesses

Quarterly estimates are advance payments on the income tax you expect to owe. For S-corp owners, this means accounting for both your W-2 withholding and the pass-through income from the business.

Most owners underpay because they estimate from their bank balance instead of from actual profit. A well-run set of books makes the difference between a guess and a calculation.

The two safe-harbor methods

You can avoid underpayment penalties by paying either:

• 90% of current-year tax — requires an accurate estimate of this year’s income
• 100% of prior-year tax — straightforward if your income is similar to last year (110% if AGI exceeded $150k)

In practice, most business owners use the prior-year safe harbor for simplicity, then catch up with a large Q4 payment when they have a clearer picture of the year.

S-corp specific considerations

Your W-2 withholding from the S-corp salary counts toward your quarterly payment obligation. If your salary has meaningful withholding, you may owe less in estimated payments than you think. This is why salary and estimates need to be looked at together.

The goal is not to minimize your quarterly payments — it’s to never be surprised by what you owe.

Business and personal return coordination

Your S-corp return (Form 1120-S) and your personal return (Form 1040) are not independent. The profit from the S-corp flows to your K-1, which flows to your 1040. The salary you paid yourself shows up in both places.

When the business return and personal return are handled separately — different CPAs, or the same CPA but without a unified view — errors and missed opportunities compound. The person preparing your 1040 needs to know what’s on the business side.

If your CPA sends you one engagement letter for the business and a separate one for your personal return with separate fees and no obvious connection — ask who’s looking at both together.

The October CPA conversation

The most valuable conversation you can have with a CPA happens in October or November — when the year is close enough to estimate accurately, but early enough to act.

What should happen in that conversation:

• Review year-to-date profit and project the full-year number
• Check whether your W-2 salary and quarterly estimates are on track
• Identify any deductions you can still take before December 31
• Decide whether a retirement contribution makes sense this year
• Confirm your Q4 estimate is sized correctly to avoid a penalty

If your CPA only contacts you in January or February when they need your documents, that’s a signal. Reactive filing is not the same as proactive planning — and the difference shows up on your check to the IRS.