Building Nigerian Payroll Compliance Into an ERP — PAYE, Pension & NHF

function calculateNigerianPAYE(grossAnnualIncome) {
  // Consolidated Relief Allowance
  const cra = Math.max(200_000, grossAnnualIncome * 0.01)
    + (grossAnnualIncome * 0.20);

  // Pension relief (8% of basic — simplified here as % of gross)
  const pensionRelief = grossAnnualIncome * 0.08;

  const taxableIncome = Math.max(0, grossAnnualIncome - cra - pensionRelief);

  // Progressive bands
  const bands = [
    { limit: 300_000,   rate: 0.07 },
    { limit: 300_000,   rate: 0.11 },
    { limit: 500_000,   rate: 0.15 },
    { limit: 500_000,   rate: 0.19 },
    { limit: 1_600_000, rate: 0.21 },
    { limit: Infinity,  rate: 0.24 }
  ];

  let remaining = taxableIncome;
  let totalTax = 0;

  for (const band of bands) {
    if (remaining <= 0) break;
    const taxable = Math.min(remaining, band.limit);
    totalTax += taxable * band.rate;
    remaining -= taxable;
  }

  return {
    taxableIncome: Math.round(taxableIncome),
    annualPAYE: Math.round(totalTax),
    monthlyPAYE: Math.round(totalTax / 12)
  };
}

function calculateNigerianPayslip(employee) {
  const gross = employee.basicSalary + employee.allowances;
  const paye = calculateNigerianPAYE(gross * 12);

  return {
    grossPay: gross,
    deductions: {
      paye: paye.monthlyPAYE,
      employeePension: Math.round(employee.basicSalary * 0.08), // PRA 2014
      nhf: Math.round(employee.basicSalary * 0.025),            // NHF Act
    },
    employerContributions: {
      pension: Math.round(employee.basicSalary * 0.10),
      nsitf: Math.round(gross * 0.01)
    },
    netPay: Math.round(
      gross - paye.monthlyPAYE
        - (employee.basicSalary * 0.08)
        - (employee.basicSalary * 0.025)
    )
  };
}