CHF 10'558 wrong, CHF 118 visible
Of all the cantons in our series, Aargau is the most uncomfortable — not because the error is most expensive there, but because it stays practically invisible.
The use case
A married couple, both working, three shared children they can claim, salaries of CHF 174'000 and CHF 157'000. The husband's payslip shows B2 — married single earner with two children. The wife's shows C0: right letter, but no children. Both should have been C3.
Calculated with the official Aargau 2026 tariffs without church tax, assuming twelve equal monthly salaries with no 13th salary and no bonus:
- Husband: 8.60 % instead of 11.60 % — around CHF 5'220 too little a year
- Wife: 14.10 % instead of 10.70 % — around CHF 5'338 too much a year
- Together: around CHF 118 too much
Why the errors cancel so precisely here
In Aargau the two effects happen to sit almost level. The wrong tariff letter on the husband's payslip deducts too little, the missing children on the wife's deduct too much — and at these salaries both amounts are nearly identical.
This is not a property of the canton. It is a property of this particular salary combination. Shift one of the salaries by a few thousand francs and the result moves noticeably; the sign can flip. Anyone deriving a rule for Aargau from this figure is wrong.
On the individual salary it very much is a problem
The wife has around CHF 445 a month deducted too much. The fact that her husband simultaneously has too little deducted changes nothing — each spouse has their own tax-at-source relationship with the canton, and nothing flows from one salary to the other.
How the Aargau tariff is built
Aargau is the first of the seven cantons to flatten out. Its scale reaches the ceiling of 27.80 % at CHF 95'001 a month — Thurgau keeps rising to CHF 150'001, Zug to CHF 200'001, Schwyz to CHF 1'000'001.
The first CHF 1'651 a month are left out of the tariff, a lower threshold than in Geneva, Zug or Schwyz, and there is a minimum of CHF 2.00 a month where the percentage would produce less.
One detail matters for salaries like the ones here. Aargau graduates in CHF 50 steps only up to CHF 10'001 a month; above that the scale moves in steps of CHF 500. Both spouses in this use case earn more than that, so both sit in the coarser part of the table — where several hundred francs of salary change nothing at all, and then a single step changes the rate applied to the entire salary.
None of this rescues the case above. Both spouses sit well inside the rising part of the scale, which is precisely where the letter and the number of children carry their full effect — and where two errors can cancel each other out on the joint account while both are still wrong.
What these figures are — and what they are not
They concern the running tax-at-source deduction, not the final tax. Because one spouse in this use case already earns more than CHF 120'000, the couple is assessed under the ordinary rules anyway — and the tax at source actually paid is credited there. The wrong code affects the household's liquidity first.
How to check your payslip
The tariff code has three parts: tariff letter, number of children you can claim, church tax marker. Check all three against your actual situation — and on both payslips, not just the conspicuous one.
A correct code is a good first check but not a complete one: with several employments the rate-determining income can be wrong too. In Aargau two errors can offset each other almost exactly, so a plausible household total is not evidence that both codes are right. If you find something, report it to HR. For years already closed, a tax-at-source correction should generally be requested by 31 March of the following year. And what you will actually owe in the end only shows once both salaries are calculated together — see our tax advisory for Aargau.
The series: the same error in other cantons
- Zurich — where children relieve the most
- Geneva — the most expensive tariff letter
- Zug — low rates, large relative deviation
- St. Gallen — both effects strong
- Thurgau — when the household pays too little
- Schwyz — the flattest tariffs
- What one child is worth — seven cantons compared