The Locum vs Substantive Calculator.

A working Excel Calculator that compares substantive (employed) and locum (sessional) arrangements side-by-side under UK 2026/27 tax and pension rules. Built for trainees considering CCST routes, salaried GPs evaluating a locum switch, and consultants weighing additional NHS sessions against private locum work.

What this Calculator is for.

A locum day rate of £800 is not equivalent to a substantive annual salary that delivers the same gross income on paper. The substantive role attracts NHS pension at 1/54 accrual; the locum work does not. The substantive role has paid leave, sick pay, and statutory entitlements; the locum work does not. The substantive role is paid through PAYE; the locum work has its own tax treatment depending on whether the practitioner works as sole-trader, partnership, or limited-company. Each of these makes a material difference to take-home income that "the headline rate" does not capture.

This Calculator does the comparison properly. The user enters the substantive offer (band, on-call, threshold) and the locum equivalent (rate per session, sessions per year, structure). The Calculator computes both under UK 2026/27 tax, pension, and NI rules, and produces a like-for-like comparison of take-home pay, pension value, and total economic value over a chosen time horizon.

What's inside.

Six sheets in a single Excel file, plus an accompanying PDF user guide.

1. Substantive — inputs for the employed role
2. Locum — inputs for the sessional/locum equivalent
3. Assumptions — the UK 2026/27 tax, NI, and pension parameters the Calculator uses
4. Comparison — side-by-side numerical comparison of the two arrangements
5. Time-horizon view — total economic value across 1, 5, and 10 years
6. Methodology — what the Calculator does and does not include in its comparison

What the inputs are.

For the substantive side: pay band, threshold, additional PAs, on-call category, employer's pension tier. For the locum side: typical session rate, sessions per year, structure (sole-trader, limited-company, partnership), expense profile. The Calculator handles the rest — UK 2026/27 income tax bands, employee and employer NI, NHS pension employee tier and employer contribution, corporation tax where applicable, dividend tax under the post-April 2026 regime.

The full set of UK 2026/27 parameters is visible in the Assumptions sheet and editable for users whose situation requires different defaults.

What you do with the output.

"The substantive role and the locum role are not the same kind of thing, even when the headline gross figures look similar. One is a contractual relationship that comes with pension accrual, statutory entitlements, and career-progression structure; the other is a market transaction in which the clinician sells sessions at a market rate and absorbs the cost of everything else. Whether the comparison favours one or the other is rarely obvious from the headline figures alone."

— from the PDF user guide, Reading the comparison

The Calculator's output supports three decisions: choosing between two specific offers, evaluating whether to leave a substantive post for a locum career, and pricing one's own locum work against the substantive equivalent the market would otherwise offer.

Who it's for.

• Trainees approaching CCST. Substantive consultant post versus locum consultant work is the first major commercial decision of consultant life. The Calculator gives you the like-for-like comparison.
• Salaried GPs considering a locum switch. A common decision; rarely made with proper analysis. The Calculator runs the analysis.
• Consultants weighing additional NHS sessions against private locum work. The marginal session, in its various forms, has very different economic value depending on how it's structured. The Calculator surfaces the difference.

What this Calculator is not.

It is a tool, not financial advice. It does not assess your specific personal circumstances, your pension forecast, or your career planning. Those require an IFA and your own judgement. The Calculator's purpose is to give you the substantive analytical input on which to base those conversations.

It uses UK 2026/27 parameters; use of the Calculator with materially different parameters requires updating the Assumptions sheet.

What's related.

• The Limited Company Decision Calculator — if the locum-side analysis points toward private work, this Calculator analyses the tax-structure decision that follows. £59.
• The Consultant Contract Evaluator — if the comparison is between two substantive consultant offers, this Calculator decomposes them in more detail. £59.