There is a specific kind of heart attack that only self-employed people get, and it arrives in a brown envelope in the spring. First year on your own tools, good year, busy year, money in the account all along. Then the return gets filed and the number at the bottom says you owe $19,000. Due now. And the account, which always seemed healthy, does not have $19,000 in it, because the money that looked like yours was spent like it was yours.
Nobody stole anything. The math was always the math. What failed was the display: a bank balance is a terrible instrument, because it shows one number with no memory of who that money actually belongs to. For a contractor, a meaningful slice of every deposit was never yours at all. The set-aside is the habit that keeps your hands off it.
The two claims on every invoice
When a client pays you, up to two governments already have claims inside that payment, and they work completely differently.
Claim one: the sales tax you collected. If you are registered to collect sales tax (GST/HST in Canada, GST in Australia and New Zealand, state and local sales tax across much of the US), your invoices carry tax on top of your price. A $5,000 job in Ontario, where 13 percent HST applies, bills at $5,650, and that extra $650 was never revenue. You are holding it in trust until your next return, minus whatever input tax credits your system lets you claim on your own purchases. This is the purest form of the trap: the money physically lands in your account, inflates the balance, and belongs to someone else from the moment it arrives. Spending it is not overspending; it is spending a third party's money. The mechanics differ everywhere: what is taxable, at what rate, how often you remit, and whether you can recover the tax on your own purchases at all. But wherever you collect tax from a client, the same rule holds: collected tax is not income.
Claim two: income tax on your profit. Employees never see this problem, because withholding happens before the money reaches them. You are your own withholding department now. Income tax, plus CPP contributions in Canada or self-employment tax in the US, comes due on your profit (revenue minus expenses), and nobody removes it as you go unless you do. If you also owe quarterly installments, and prior-year balances can put you there, the due dates come around faster than April.
Two claims, two behaviors: sales tax is a fixed, knowable percentage of every invoice; income tax is a percentage of profit you have to estimate. Which is why the set-aside has two parts.
How do you build your own percentage, using Canadian numbers?
Rules of thumb are only trustworthy when you have seen one built. Any worked example has to pick a jurisdiction, because the arithmetic needs real rates, so this one is Canadian: a fictional solo electrician in Ontario. If you work in the US, Australia or New Zealand, nothing about the method changes and every number does. Substitute your own sales-tax rate and your own income-tax and self-employment position, run the same three steps, and you will land on your own percentage. Every figure below bends by country, province or state, and situation, so rebuild it with your own figures and check it with your accountant.
Marta's year:
- Invoiced work: $160,000, plus $20,800 of HST collected at 13 percent.
- Business expenses: $60,000 of materials, van, insurance, tools and phone, on which she paid about $6,000 of HST.
- Profit: $160,000 minus $60,000 = $100,000.
Her sales-tax position: $20,800 collected minus roughly $6,000 in input tax credits leaves about $14,800 to remit across the year.
Her income-tax position: on roughly $100,000 of self-employed profit in Ontario, combined federal-provincial income tax plus CPP lands, ballpark, in the high-$20,000s. Call it $28,000.
Now convert both into set-aside habits:
- The sales tax is not a rule of thumb; it is exact. Every invoice shows the tax as its own line. That amount, 100 percent of it, moves aside on receipt. Her ITCs mean she will remit less than she collected, and the difference flows back to her at filing, a pleasant surprise instead of a catastrophic one.
- The income tax becomes a percentage of her pre-tax invoice amounts. $28,000 of tax on $160,000 of billings is 17.5 percent. Add margin for error and installment interest, and Marta's rule is: move 20 percent of every invoice's pre-tax amount, plus the entire tax line, into a separate account, the day the payment lands.
On a $5,650 payment ($5,000 plus $650 HST), that is $650 plus $1,000: $1,650 set aside, $4,000 truly hers. Notice how different that is from the bank-balance view, which cheerfully reported $5,650 of new money.
A rough calibration for the income-tax percentage if you have no history yet: thin-margin or heavy-expense businesses might justify 15 percent of billings; a typical established solo trade lands near 20; a high-margin, low-expense year, or a higher bracket, can justify 25 to 30. Your first accountant conversation and your first filed return will tune it. Err high for a year; the punishment for over-saving is a refund to yourself.
"Every check that comes in, I move the tax line plus twenty percent before I count the rest. What's left is real. The account I moved it to isn't mine, it just lives at my bank."
The separate account is the whole mechanism
The percentage is arithmetic; the account is psychology, and the psychology is the part that fails in practice.
A set-aside that lives as a mental note inside your main account does not exist. The balance you see is the balance you feel, and in a lean February, with payroll-less payday pressure and a supplier bill due, the mental note loses to the visible number every time. The fix costs nothing:
- Open one more account, at your existing bank, and name it something honest: Tax. Some banks let you nickname it; "Not Mine" has kept more than one contractor honest.
- Move the money on receipt, not on schedule. The transfer is part of processing a payment, like recording it against the invoice. Money that pauses in the main account first gets absorbed; the whole trick is that it never visits.
- Withdrawals go to exactly one payee. The government, at remittance and installment dates. The day that account funds a transmission repair "just this once," the system is over, because the precedent is set and February always comes back.
- Surplus stays put until filing. If your percentage was too high, the filing tells you, and the excess is a bonus with your name on it. That asymmetry (over-saving becomes a windfall, under-saving becomes a debt with interest) is the entire argument for rounding up.
The separate account also solves a problem the percentage alone cannot: lumpy income. Trade revenue does not arrive in twelve even slices; it arrives as a $14,000 month, then a $3,000 month, then two good ones. A contractor who plans to "save up for taxes when things are good" discovers that good months have their own spending plans (a tool upgrade, catching up on bills from the thin month), and the saving never quite starts. The per-payment transfer sidesteps the whole psychology: the set-aside scales itself automatically. Big month, big transfer; thin month, small one. No month ever requires a willpower decision, because the decision was made once, back when no particular dollar was at stake.
Contractors sometimes resist this as money "sitting idle." It is the opposite of idle: it is doing the single highest-value job money can do in a small business, which is making the balance you look at every day tell the truth.
How do you keep the number honest all year?
The last failure mode is drift. You set 20 percent in March, business changes, expenses spike or a big contract lands, and by November the honest number is 24 and you are still moving 20. The defense is visibility: the set-aside is not a decision you made once; it is a number you glance at monthly.
Three glances cover it:
- Collected tax versus set-aside tax. The sales-tax line across your invoices for the period, against what actually moved to the tax account. These should match to the dollar; a gap means the habit slipped.
- Profit trend versus percentage. If margins are running fatter than the year you calibrated on, your income-tax percentage is stale on the low side. Fatter profit means a bigger slice owed.
- Installment calendar. Once you are in installment territory, the due dates (quarterly in Canada, a similar rhythm for US estimated taxes) are cash-flow events to see coming, not envelopes to be surprised by.
This is a place software genuinely helps, because the inputs already exist in your records. Zeus puts a tax set-aside chart on the home dashboard: it reads the tax collected across your invoices and shows continuously what should be sitting in that separate account. The target is a number you see between jobs rather than reconstruct in April. Your invoices, payments and receipts feed it as you work; the glance replaces the spreadsheet.
The brown-envelope heart attack is completely optional. The money was always leaving; the set-aside just makes it leave in weekly slivers you never miss, instead of one spring amputation you never forget.
Frequently asked questions
What percentage should I use if this is my first year and I have no numbers?
Start at the tax line plus 25 percent of pre-tax billings and treat it as deliberately high. First years are exactly when surprises cluster: registration thresholds, installments triggered for next year, an accountant finding less deductible than you hoped. If filing shows you over-saved, the surplus is yours and next year's percentage comes down calibrated. Confirm the starting point with an accountant; one short conversation beats a year of guessing.
Do I set aside from every payment, even deposits and partial payments?
Yes, and deposits especially. A deposit carries its share of tax, and GST/HST is generally accounted for when an amount becomes due or is paid, not when you eventually finish the job (timing details vary; ask your accountant). Practically, applying the habit to every dollar that arrives (deposits, partials and final payments alike) is also what keeps it a reflex instead of a judgment call.
What if I'm behind already and there's a tax debt?
Two moves, in order. First, start the set-aside today at the full rate on all new revenue, or the hole keeps deepening under you while you bail. Second, contact the tax authority about a payment arrangement rather than going quiet; both the CRA and IRS deal with payment plans routinely, and interest on an acknowledged debt with an arrangement beats penalties on an ignored one. An accountant is worth their fee in exactly this situation.
Should the set-aside account earn interest?
If it is easy, sure: a high-interest savings account at your bank is a fine home for it, and the interest is a small bonus (taxable itself, note). But do not let optimizing the yield add friction to the transfer or put the money somewhere slow to access at remittance time. The account's job is behavioral, not financial: it exists to keep one honest number in front of you, and the day-one transfer habit matters a hundred times more than the rate.
ZEUS