net 13th salary brazil
The net 13th-salary surprise never happens on the first installment, which has no deductions: it shows up in December, when INSS and IRRF land entirely on the second one.
The R$ 988.09 INSS deduction already hits the R$ 8,475.55 ceiling, so the deduction stops growing even if the base salary were even higher.
With only 7 twelfths, the gross 13th salary drops to R$ 5,250.00 and IRRF plunges to R$ 20.12, because the taxable base sits much closer to the exemption bracket than in the full-year scenario.
Fewer twelfths do not cut IRRF proportionally: it pushes the taxable base out of the 27.5% bracket and almost into the exemption zone, so the tax falls much faster than the gross amount.
Avos are the monthly fractions that make up the 13th: each complete month worked in the year is worth 1/12 (one avo), and a fraction of 15 days or more within a month also counts as a full avo. Someone who worked the whole year accumulates 12 avos and receives the full 13th, while someone who worked part of the year receives it proportionally. The calculator uses that number to multiply the salary by avos/12 and reach the gross 13th.
Because the 1st installment is half the gross amount with zero deductions, while the 2nd carries the entire INSS and IRRF calculated on the full 13th salary, on top of subtracting what was already advanced in the 1st.
Not at the same rate: in the R$ 9,000.00 example, dropping from 12 to 7 twelfths cuts gross pay by 41.7%, but IRRF falls by more than 98%, because the smaller taxable base exits the highest tax bracket.
Only if the fraction worked in that month is 15 days or more, a rule set by Decreto 57.155/1965; working fewer than 15 days in a month does not secure that twelfth.
⚠️ Educational simulation. The 1st installment has no income-tax deduction. The 2nd installment has INSS and IRRF for the December period.
2026 tables: INSS, Portaria MPS/MF 2/2025. IRRF, Law 15.191/2025 and Law 15.270/2025 (exemption up to BRL 5,000 gross).
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