Package ukmoneycalc on DUB

A small, dependency-free D library for UK take-home-pay math (2025/26): income tax with the personal-allowance taper, Class 1 National Insurance, student-loan repayments, and a full gross-to-net breakdown.

To use this package, run the following command in your project's root directory:

ukmoneycalc

A small, dependency-free D library for UK take-home-pay math — the deductions that turn a gross salary into the net figure that lands in your bank account, for the 2025/26 tax year (England / Northern Ireland).

It computes each PAYE deduction from first principles: income tax with the personal-allowance taper, Class 1 employee National Insurance, and student-loan repayments — then sums them into a full gross → net breakdown.

The thresholds and worked examples mirror the model used at ukmoneycalc.com.

Why

Take-home pay is not just "salary minus a tax rate". Three independent charges stack on top of each other, each with its own thresholds:

net = gross − income tax − National Insurance − student loan

The awkward parts are the personal-allowance taper (you lose £1 of the £12,570 allowance for every £2 earned over £100,000, so the marginal rate spikes to 60% in that band) and the two-rate NI structure. This library handles both exactly.

Install

Add it to your dub.json:

"dependencies": {
    "ukmoneycalc": "~>0.1.0"
}

Usage

import ukmoneycalc;
import std.stdio;

void main()
{
    auto t = takeHome(60_000, StudentLoanPlan.plan2);

    writeln("gross:        ", t.gross);              // 60000
    writeln("income tax:   ", t.incomeTax);          // ~11,432
    writeln("NI:           ", t.nationalInsurance);   // ~3,210.60
    writeln("student loan: ", t.studentLoan);         // ~2,837.70
    writeln("net / year:   ", t.net);
    writeln("net / month:  ", t.netMonthly);
    writeln("deducted:     ", t.effectiveRate);       // fraction of gross
}

API

Symbol	Description
`personalAllowance(gross)`	Tax-free allowance (£12,570), tapered £1 per £2 over £100k, gone by £125,140.
`incomeTax(gross)`	2025/26 income tax: 20% / 40% / 45% on taxable income.
`nationalInsurance(gross)`	Class 1 employee NI: 8% to £50,270, 2% above.
`studentLoan(gross, plan)`	Plan 1 / 2 / 4 / 5 (9%) or Postgraduate (6%) repayment above threshold.
`takeHome(gross, plan = none)`	Full `TakeHome` breakdown: tax, NI, loan and net.
`TakeHome.netMonthly`	Net annual pay ÷ 12.
`TakeHome.effectiveRate`	`(gross − net) / gross` as a fraction.

2025/26 thresholds

Item	Value
Personal allowance	£12,570 (tapers over £100,000)
Basic rate (20%)	first £37,700 of taxable income
Higher rate (40%)	up to £125,140
Additional rate (45%)	above £125,140
NI primary threshold	£12,570
NI upper earnings limit	£50,270
NI rates	8% then 2%

Worked example: a £30,000 salary pays £3,486 income tax and £1,394.40 NI, leaving £25,119.60 net (~£2,093/month), an effective deduction of ~16.3%.

Build & test

dub build
dub test

Requires a D compiler (DMD or LDC) and DUB. Every public function is @safe pure and the package has no dependencies.

License

MIT — see LICENSE.

0.1.0	2026-Jul-16
~main	2026-Jul-16

ukmoneycalc 0.1.0