By: Sharon Heinz, EA

Date Posted: September 2026

Reading Time: 8 – 10 Minutes

If your income moves up and down from month to month, tax season probably doesn’t feel like a single deadline — it feels like a moving target you’re never quite sure you’ve hit. One quarter you’re flush and confident. The next, revenue dips and you’re wondering if the money you set aside for the IRS is still going to be enough.

That uncertainty is one of the most common sources of stress we see in business owners with variable income. The good news: it’s also one of the most fixable. With the right system, you can stop guessing and start knowing, regardless of how unpredictable your revenue can be.

When your income is steady, tax planning is fairly straightforward: figure out your rate, save a consistent amount, done; however, most business owners don’t have that luxury. A strong month can be followed by a slow one. A big client payment might land in one quarter and nothing in the next.

The problem is that many owners still try to apply a flat, fixed-dollar savings plan to income that isn’t flat at all. That mismatch is exactly what creates cash-flow anxiety. Business owners either save too little during good months and come up short later, or lock away too much during a strong stretch and feel the pinch when cash gets tight. Neither extreme serves you well, and both are avoidable with a plan built around how your income actually behaves.

The widely cited rule of thumb is to set aside roughly 25–30% of your net profit for taxes. That range generally covers two things:

• Self-employment tax — a flat 15.3% that covers Social Security and Medicare for sole proprietors, partners, and single-member LLC owners. This is the “employer half and employee half” you’d normally split with a boss, except now you’re covering both sides yourself.
• Federal income tax — this is where things get more personal. Your rate depends on your filing status, deductions, credits, and how much of your income you’re reinvesting in the business. If you’re in a state with its own income or business tax, that adds another layer on top.

At lower income levels, 25% is often a reasonable starting point. As profit climbs, particularly past six figures, it’s common to shift closer to 30%, since additional taxes and phase-outs can start to apply.

Here’s the part that doesn’t get said enough: 25–30% is a starting point, not a guarantee. It’s a helpful default when you don’t yet have better information, but it isn’t calibrated to your actual situation.

In the early years of a business, deductions and credits can significantly reduce what you owe, some new businesses end up with little to no income tax liability at all in their first year or two. Setting aside 30% in that scenario means tying up cash you didn’t actually need to set aside. On the flip side, if your deductions are limited or your state has meaningful business taxes, 30% might not be enough.

The real answer isn’t a single percentage that applies to every business. It’s a percentage based on your numbers, such as your deductions, your entity structure, your state, and your history. That’s the difference between a rule of thumb and an actual plan.

Knowing your target percentage only helps if you actually set the money aside consistently. Here’s a simple framework that works especially well when profits fluctuate:

1. Open a dedicated tax savings account. Keep it completely separate from your operating account. A mental note doesn’t count! Money that’s easy to “borrow from” during a slow month usually gets borrowed when it is all put in the same account.
2. Save a percentage, not a fixed dollar amount. Because your target is a percentage of what comes in, your tax savings naturally scale with your income. A big month means a bigger transfer; a slow month means a smaller one. This single shift removes most of the guesswork, and most of the anxiety.
3. Automate the transfer. Whether it’s triggered weekly, biweekly, or with every deposit, taking the decision out of your hands means the money is already set aside before you’re tempted to use it elsewhere.
4. Revisit your percentage periodically. As your deductions, income level, and entity structure evolve, your ideal set-aside rate will too. What made sense in year one may not make sense in year three.

Setting money aside solves half the problem. Paying it to the IRS on schedule solves the other half. The IRS expects estimated tax payments four times a year:

Dates shift slightly when the 15th falls on a weekend or holiday.

Missing a quarterly payment (or an underpaying one) can trigger an underpayment penalty, even if you end up owed a refund when you file your return. The IRS calculates that penalty based on when the money was due, not just whether it eventually got paid. For a business with variable income, this is often the trickiest part; it’s tempting to base a quarterly payment on how one particular quarter went financially. The more reliable approach is to base it on your full-year projection or last year’s actual liability.

We regularly meet business owners who had a genuinely good year and were still caught off guard at tax time due to lack of savings and quarterly payments. Beyond the tax itself, types of costly scenarios typically come with:

• Penalties for late payment and missed quarterly estimates
• Interest that accrues on the unpaid balance until it’s resolved
• Fees if a payment plan becomes necessary
• The mental and emotional toll of a surprise bill you have to scramble to cover

Compare that to the alternative: a percentage-based savings plan, an automated transfer, and four quarterly payments made on time. It takes far less effort than sorting out a problem after the fact, and it removes the anxiety of not knowing where you stand.

Variable income doesn’t have to mean variable stress. The owners who feel most in control aren’t the ones with the steadiest revenue, and they’re the ones with a plan that flexes when their revenue does.

If you’re not sure whether you’re setting aside the right amount, or if quarterly payments feel like a moving target every time they come around, that’s exactly what proactive tax planning is for. We’ll look at your actual number, such as your entity structure, deductions, and income patterns, and help you land on a set-aside percentage and payment schedule built for how your business really runs, not a generic rule of thumb.

Ready to stop guessing at tax time? Reach out to Profit Wise Accounting, and let’s build a system that keeps you ahead of every quarterly deadline — no matter how your revenue moves.

Sharon Heinz, EA, is the owner of Profit Wise Accounting. Profit Wise provides tax preparation, strategic tax planning, accounting, bookkeeping, payroll, and business advisory services for small and growing businesses.