Free calculators for running a business in the UK
Whether you trade as a sole trader or through a limited company, the same money questions come round every year: how to pay yourself, what National Insurance the payroll will cost, how much relief a purchase earns, what the premises will cost in rates, and what to charge. These UK business calculators cover nine of those questions using the current tax rules, and each one shows its working, so you can see where a number comes from before you rely on it.
All nine calculators are free to use, with no sign-up, and they run entirely in your browser. Nothing you enter is uploaded, stored or shared, so you can model your real figures and compare scenarios side by side.
Structure and paying yourself
The sole trader vs limited company calculator runs one figure of annual profit through both structures. The sole trader side pays Income Tax and Class 4 National Insurance on the whole profit; the company side pays employer National Insurance on the director’s salary, Corporation Tax on what remains and dividend tax on what is distributed, and it can leave profit retained in the company. Because the director’s salary changes the answer more than anything else, it is an input you can move, and trying the secondary threshold, the personal allowance and a higher figure shows how quickly the gap opens or closes.
Directors are the one group whose National Insurance an ordinary payroll calculator gets wrong. The directors National Insurance calculator applies the annual earnings period, pro-rates the thresholds for a mid-year appointment, and compares the result with the standard employee method, which shows why a large annual bonus costs a director more than it would cost an ordinary employee. The Employment Allowance calculator works out how much of the employer National Insurance bill the allowance covers for 2026/27 and how much goes unused, keeps Class 1A on benefits in kind separate because the allowance cannot touch it, and flags the single-director rule that shuts many one-person companies out.
Reliefs on investment and innovation
The Annual Investment Allowance calculator works through capital allowances in the order the legislation applies them: the Annual Investment Allowance first, set against special-rate spend where relief is otherwise slowest, then full expensing and the first-year allowance for companies buying new and unused assets, then writing-down allowances on whatever is left. It pro-rates for a short accounting period, limits the tax saving to the profit available, and shows the pool balance you are still waiting to relieve. The R&D tax credit calculator values a research claim under the merged expenditure credit scheme, tests whether Enhanced R&D Intensive Support is open to a loss-making SME that meets the intensity test, and shows which route pays more.
Premises and getting paid
The business rates calculator estimates the annual bill on a property in England from its rateable value, choosing the right multiplier and applying Small Business Rate Relief, including the taper between full relief and none. Wales, Scotland and Northern Ireland set their own multipliers and reliefs, so a property there needs its own nation’s figures. The late payment interest calculator works out what you can claim when a business customer pays late under the Late Payment of Commercial Debts (Interest) Act 1998: simple interest at the Bank of England base rate plus the statutory margin, the fixed compensation sum for the size of the debt, and any reasonable recovery costs above it, with the daily interest shown for your chasing letter.
Pricing and planning
The break-even calculator takes fixed costs, a selling price and a variable cost per unit, and returns the units and revenue needed before profit begins, with the contribution each sale makes. The profit margin and markup calculator shows profit per unit, margin and markup from one cost and one price, which prevents the classic mistake of applying a markup when you meant a margin. Enter figures net of VAT in both, since VAT is collected on HMRC’s behalf and is not part of your profit.
Why run the numbers first
Most of these choices are costly to undo. Incorporating brings filing obligations and accountancy fees as well as a different tax bill, a bonus paid in the wrong way can cost a director avoidable National Insurance, buying equipment just before or just after a year end changes when the relief arrives, and an overdue invoice left unchased costs a little more every day. Seeing the figures in advance lets you change the salary, the timing of a purchase or the price before the decision is made rather than after.
The rates, thresholds and allowances the tools rely on are stored as parameters for 2026/27 and updated when they change. The results are estimates for planning, not tax or legal advice: your own position depends on facts the calculators cannot see, such as associated companies, the exact nature of each asset or the terms of your contract, so check anything material with an accountant, HMRC or a solicitor.
Where to start
- Deciding on a structure: compare sole trader and limited company, then test director pay with the National Insurance tool.
- Taking on staff: check the Employment Allowance before you set salaries.
- Buying equipment or investing in research: value the relief before the year end.
- Taking on premises or chasing a debt: estimate the rates bill or the late payment claim.
Used together, the nine calculators take a business from its price list to its year-end tax computation, and they show at each step which decision moves the result most.
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