dutch-tax-income-calculator-npm

NPM package with functionality to calculate Dutch Tax Income

Installation

npm install --save dutch-tax-income-calculator

Usage

The package exports three members: SalaryPaycheck (gross → net), netToGross (net → gross), and constants (the underlying tax tables).

Gross to net (SalaryPaycheck)

import { SalaryPaycheck } from 'dutch-tax-income-calculator';

const paycheck = new SalaryPaycheck(
  {
    income: 36000,
    allowance: false,
    socialSecurity: true,
    older: false,
    hours: 40,
  },
  'Year',
  2026,
  { checked: false }
);
console.log(paycheck);
/* OUTPUT:
{
  grossHour: 17.31,
  grossDay: 141.18,
  grossWeek: 692.31,
  grossMonth: 3000,
  grossYear: 36000,
  inputGrossYear: 36000,
  taxFreeYear: 0,
  grossAllowance: 0,
  taxableYear: 36000,
  taxFree: 0,
  payrollTax: -2916,
  payrollTaxMonth: -243,
  socialTax: -9954,
  socialTaxMonth: -829.5,
  taxWithoutCredit: -12870,
  taxWithoutCreditMonth: -1072.5,
  labourCredit: 5498.04,
  labourCreditMonth: 458.17,
  generalCredit: 2714.29,
  generalCreditMonth: 226.19,
  taxCredit: 8212.33,
  taxCreditMonth: 684.36,
  incomeTax: -4657.67,
  incomeTaxMonth: -388.14,
  netYear: 31342.33,
  netAllowance: 0,
  netMonth: 2611.86,
  netWeek: 602.74,
  netDay: 122.91,
  netHour: 15.07
}
*/

new SalaryPaycheck(salaryInput, startFrom, year, ruling):

• salaryInput.income: gross amount, denominated in whatever unit startFrom specifies
• salaryInput.allowance: whether income already includes the 8% holiday allowance (vakantiegeld)
• salaryInput.socialSecurity: whether social security contributions apply
• salaryInput.older: whether the person has reached retirement (AOW) age
• salaryInput.hours: contracted hours per week
• startFrom: 'Year' | 'Month' | 'Week' | 'Day' | 'Hour' — which unit income is expressed in
• year: tax year to calculate for (see constants.years for supported years)
• ruling: { checked: boolean, choice?: 'normal' | 'young' | 'research' } — the 30% ruling (30%-regeling)

Net to gross (netToGross)

Given a target net income, finds the gross salary that produces it:

import { netToGross } from 'dutch-tax-income-calculator';

const result = netToGross(
  {
    amount: 31342.33,
    field: 'netYear',
    holidayAllowanceIncluded: false,
  },
  {
    period: 'Year',
    year: 2026,
    allowance: false,
    socialSecurity: true,
    older: false,
    hours: 40,
    ruling: { checked: false },
  }
);
console.log(result.grossYear); // 36000

netToGross(target, options):

• target.amount: the net figure to solve for
• target.field: 'netYear' | 'netMonth' — which net field amount refers to
• target.holidayAllowanceIncluded: whether amount already includes the holiday allowance payout (netAllowance)
• options: the same shape SalaryPaycheck accepts, except period replaces startFrom and must match target.field ('Year' for netYear, 'Month' for netMonth)

netToGross returns the full SalaryPaycheck result computed at the solved gross — the same shape as the forward calculation above. Because every internal amount is rounded to 2 decimals, more than one gross value can occasionally round to the identical net; in that case netToGross returns { grossLow, grossHigh } (the plateau bounds) instead of guessing a single number. If no gross produces the target net, it throws an error naming the nearest achievable net.

Constants

import { constants } from 'dutch-tax-income-calculator';

Exposes the underlying tax tables and thresholds used for the calculation — years, rulingThreshold, rulingMaxSalary, lowWageThreshold, payrollTax, socialPercent, generalCredit, labourCredit, and more (see data.json).