A healthy operating balance can hide an underfunded tax reserve, especially right after a strong month. You still need to set aside money for taxes. The operating balance looks fine after you close the books, but no portion of it has been earmarked for the quarterly estimate and payroll tax deposit, even though both are due in the next few weeks.
At $1M–$6M with employees, the solopreneur rules of thumb stop holding. Tax money left in the operating account reads as spendable cash on the dashboard. Set the tax share aside before that cash becomes part of day-to-day spending, then use account structure to keep it out of operating decisions.
Why setting aside money for taxes gets harder as you grow
Setting aside taxes gets harder as you grow because cash volume increases while your single mental estimate doesn't, and payroll obligations enter the mix once you have a team. Three shifts drive the change:
Committed cash looks available. When large deposits and outflows run through a single operating balance, the portion that belongs to the IRS looks no different from the rest, so it can quietly get spent on a hire or a vendor prepayment before you realize it was already committed.
Revenue swings widen the estimate gap. A rough Q1 and a breakout Q3 can carry very different liabilities, and a number you set in January stops matching reality by summer. If you only estimate once a year, you're betting that the balance will cover a bigger bill later.
The IRS charges interest that compounds. Under-reserving creates a measurable interest cost that grows every day the shortfall goes unpaid, on a base that's already larger because you're earning more.
The Internal Revenue Service (IRS) charges interest on underpaid tax. The current rate is 7% per year, compounded daily, for the quarter beginning July 1, 2026—a figure that changes quarterly, so check IRS.gov's quarterly rates page before you lock in a number. Compounded daily means the cost of under-reserving grows every day the shortfall goes unpaid, and it grows on a base that's already larger because you're earning more.
Move the tax portion as revenue arrives
Money that lands in a separate account the moment it arrives can't be spent as operating cash, because it's no longer sitting in the operating account. Separating the cash turns the intention into a funded account you can use when the payment comes due. This is the pattern Relay is built around—a percentage of every deposit moves into a dedicated account before it becomes operating cash. If you want to understand what under-reserving can cost, the mechanics of quarterly tax penalties are worth knowing before you set your percentage.
Sizing your tax set-aside
No single percentage works for every business, but most owners at this revenue tier should plan from their accountant's estimate of tax on net income—not a widely repeated solopreneur shortcut. The tax allocation often associated with the Profit First method is presented as part of a revenue-tiered framework for small businesses, including guidance for both smaller and larger businesses. At higher revenue with employees, your effective rate and entity structure usually push the working baseline higher, depending on your accountant's calculation.
Start from a baseline and true it up against your actual liability, because a handful of specific factors move the number.
Entity structure. Tax treatment changes by entity structure; for example, an S corporation (S-corp) and a C corporation (C-corp) don't produce the same bill on the same net income.
Marginal rate at higher income. As net income climbs, more of it is taxed at higher marginal rates, so a percentage that fits at lower income can under-reserve at higher income.
State tax obligations. State income tax stacks on top of federal, and the combined rate varies widely by where you operate.
The qualified business income (QBI) deduction. It can lower the effective rate for some pass-through owners, which pulls the working percentage down rather than up.
Owner W-2 withholding. If you take a salary and withhold from it, your W-2 withholding already covers part of your personal liability, which changes how much the separate set-aside needs to carry.
At this tier, most owners land well above the solopreneur figures. Pick a defensible baseline with your accountant, then adjust it against your real numbers rather than treating any single percentage as fixed.
Coordinating tax set-asides with payroll tax deposits
Payroll tax deposits and estimated income taxes are separate obligations on separate schedules, and your set-aside system needs to account for both. Solopreneur guidance usually skips payroll deposits because owners without employees don't make employer payroll tax deposits. Once you have a team, you're holding cash for at least three separate tax obligations at once, and treating them as one pool can cause you to under-reserve one category without noticing.
Employer payroll tax deposits. These go to the IRS on your assigned deposit schedule (monthly or semi-weekly), covering withheld income tax and both halves of Social Security and Medicare. They're tied to payroll and stay separate from your personal return.
Owner-level estimated income tax. Paid quarterly, this covers your personal liability on business income. You generally owe estimated payments if you expect to owe $1,000 or more as an individual, or $500 or more as a corporation, after subtracting withholding and credits (IRS Estimated Taxes).
The tax reserve you build from each deposit. You accumulate the tax reserve throughout the quarter so the estimated payment is funded before it's due, rather than pulled together at the deadline.
If you're an S-corp owner, the W-2 salary you pay yourself already has withholding on it, which covers part of your personal liability. That means your separate estimated set-aside can be smaller than the headline percentage suggests. Work the withholding-and-estimated-payment split out with your accountant, or you'll over-reserve on one side while under-funding the other. Holding both obligations in a single mental bucket is a common reason profitable businesses end up short on one of them.
Safe harbor after a breakout year
Safe harbor protects you from the underpayment penalty, and a big prior year raises the floor it sets. The IRS lets you avoid the penalty if you pay enough under its safe harbor rules. The required amount is 90% of your current-year tax or 100% of your prior-year tax. The prior-year safe harbor figure climbs to 110% if your prior-year adjusted gross income was over $150,000 (IRS Topic 306). If your business is growing, the 110% threshold is usually the one that applies.
A breakout prior year can raise the safe harbor floor even when current-year income falls. If last year was a breakout and this year normalizes back to something more modest, your current-year projection might suggest a smaller reserve, but the prior-year safe harbor still uses last year's number. To stay penalty-safe, you may need to pay 110% of a liability that was inflated by a year you're not repeating. A percentage of current income alone would leave you short, and the shortfall accrues interest.
Compare both safe harbor numbers throughout the year: your current-year projection and your prior-year liability. Then reserve to the higher of what the two tests require. Reserving to a percentage of current income works in a steady year, but after a spike, that approach can leave the account under-funded.
By the end of Q2, you have enough actual results to adjust before the deadline pressure hits. Compare your live projection against the prior-year floor, then raise or lower the back-half set-aside. Treat your set-aside percentage as an adjustable number as the year clarifies.
Automating your tax set-aside so the money is already there
Automating a percentage transfer into a separate tax account on every deposit makes the set-aside reliable. Manual transfers depend on you remembering to move money during the busiest stretch of the month, which is exactly when the transfer gets skipped. A rule that fires on its own removes the decision from the month-end workload.
Relay is built for this. You can open dedicated checking accounts for taxes, operations, and payroll, so each obligation lives in its own account instead of one shared balance. Relay's automated transfer rules move a set percentage of every incoming deposit into the account you choose, so the tax reserve fills as revenue lands. Setting up multiple checking accounts gives the separation a structural home instead of leaving it as a running total in your head.
Setting up the tax account and transfer rule is a one-time routine.
Open a dedicated tax account, kept separate from both operating and payroll cash.
Set a percentage transfer rule sized to your working baseline on incoming deposits.
Route that transfer to the tax account automatically, so it fires on every deposit without your involvement.
Reconcile the accumulated balance against your actual quarterly obligation, and adjust the percentage as income varies.
Once the setup's in place, the reserve builds on its own, and your only recurring task is updating the percentage when your numbers move.
Build the set-aside into how money moves
At this revenue tier, separate accounts and automatic transfers are more reliable than remembering to move tax money manually. Your baseline still needs to match your entity structure and prior-year floor, and your real liability should true up the percentage as the year changes.
The estimated payment is easy when the cash is already waiting for it. Opening a Relay account gives you dedicated checking accounts for taxes, payroll, and operations, plus percentage-based transfer rules that move tax money in as deposits arrive—so the reserve is ready when the deadline hits.
Frequently asked questions
What percentage of income should a small business set aside for taxes?
At this revenue tier, your set-aside should usually be based on your accountant's estimate of tax on net income, not a solopreneur shortcut. Your entity structure and marginal rate set the baseline. State taxes and owner W-2 withholding can move the final percentage. Set a baseline with your accountant and adjust it against your actual numbers.
Do I still owe quarterly estimated taxes if my S-corp already withholds from my salary?
Often yes, but usually less than a flat percentage would suggest. The withholding on your W-2 salary covers part of your personal liability, so your separate estimated payments only need to cover the remainder, typically the tax on pass-through income beyond your wages. Work the exact split with your accountant, because over-withholding on salary and under-paying estimates both create problems.
Are payroll tax deposits the same as quarterly estimated taxes?
No. Payroll tax deposits are employer obligations tied to your team's wages, paid to the IRS on a monthly or semi-weekly deposit schedule. Quarterly estimated taxes cover your personal income tax liability on business earnings. They're different money on different schedules, and holding them in one pool is a common way to under-reserve one of them.
What happens if I don't set aside enough and underpay?
The IRS charges interest on the underpaid amount, and that interest compounds daily until the shortfall is paid. Because the rate applies to a larger base as your income grows, under-reserving gets more expensive at higher revenue. Safe harbor rules can protect you from the penalty if you pay a set share of current-year or prior-year tax, which is why sizing your reserve to the higher floor matters.
Should tax money sit in checking or savings?
Keep tax money in a dedicated account, whether that's checking or savings. The goal is to keep the reserve out of the daily spending balance. An account that fills automatically on each deposit is more reliable than tracking a mental reserve inside your main balance.
