13th Salary Calculator

How to use

1. Type your gross monthly salary and, when overtime or commissions are habitual, the monthly average of that variable pay.
2. Say how many full months you worked this year and how many days you worked in the month you joined or left: 15 days or more turn that month into a whole twelfth.
3. Read the two instalments side by side, and open the panel below to edit any figure — the tax bands, the reducer, the INSS bands, even the 15-day rule.

About this tool

The 13th salary is a full extra month of pay, earned one twelfth at a time. Every month under a CLT contract adds a twelfth, and a month you did not work in full still counts as a whole one if you were there for 15 days or more — the rule in article 1, paragraph 2 of Lei nº 4.090/1962, and the reason someone hired on the 16th of June still takes seven twelfths in December. The base is not only the contract salary: overtime, commissions and the night premium enter it as a monthly average when they are habitual, which is why this page asks for that average separately.

What surprises people is how the money is split. The first instalment is an advance, paid between 1 February and 30 November, and it comes with no deduction at all — half the 13th lands in the account untouched. Everything is then charged against the second instalment, due by 20 December: the INSS contribution and the income tax withholding, both worked out on the whole 13th and never on the half being paid. A calculator that charges each instalment on its own half shows a December payment that looks generous and is wrong, because the progressive tables bite harder on the full amount than on half of it. This page keeps the two instalments apart and adds them up, so the arithmetic behind December is visible before December arrives.

The 13th is also taxed on its own: its own INSS calculation with its own ceiling, its own reading of the income tax table, its own comparison between the legal deductions and the simplified discount, and it is never added to the December salary before the tax is worked out. Your employer deposits FGTS on it too — 8% paid on top, never deducted from you. Not included here: union dues, health plan co-payments, an advance taken during your holiday and anything a collective agreement adds. Everything is computed on your own device and nothing you type is sent anywhere.

The formula

Twelfths = full months worked + one more when the incomplete month reaches 15 days, capped at 12. Gross 13th = (monthly salary + average variable pay) × twelfths ÷ 12. First instalment = 50% of the gross 13th, with no deduction. INSS = rate of the band × the whole gross 13th − the deduction parcel of that band, limited by the contribution ceiling. Income tax base = the whole gross 13th − INSS − dependants − alimony, or the gross 13th − the simplified discount, whichever produces less tax; the exemption reducer of Lei nº 15.270/2025 is then taken off the tax and can never make it negative. Second instalment = gross 13th − first instalment − INSS − income tax. Amounts are held as whole cents and each payslip line is rounded once, half up.

Frequently asked questions