Free calculators for the questions UK small businesses have to answer more than once: what a hire actually costs, what you can legally charge on a late invoice, whether an electric car still stacks up through the company, and what April’s changes did to your numbers.
Every tool on this page uses one shared set of rates, checked against HMRC, gov.uk and Bank of England sources, with the date of the last check printed on the calculator itself. When April or a Budget moves a figure, it moves in one place and every tool follows — so you will not find one page here quoting last year’s minimum wage while another quotes this year’s.
- Cost of an Employee CalculatorWhat a hire really costs once NI, pension and holiday are counted.Open the calculator →
- Late Payment Interest CalculatorStatutory interest and compensation you can legally add to an overdue invoice.Open the calculator →
- Company Car Tax CalculatorBIK and salary sacrifice on an electric company car, against the petrol or diesel it replaces.Open the calculator →
- Budget Impact CalculatorWhat the April 2026 changes added to your wage bill and your tax.Open the calculator →
Why these four
They are the sums small business owners tell us they redo every year and never quite trust. The cost of an employee changed character in April 2025, when employer National Insurance went to 15% and the threshold fell to £5,000, and most owners are still working from a mental model formed before that. Late payment interest is a right almost nobody exercises, largely because the calculation looks harder than it is. Company car tax on an EV is the one genuinely large tax break still available to an owner-managed business, and it is shrinking on a published timetable. And every April a set of changes lands that is easy to read about and hard to translate into your own payroll.
How to read the numbers
Each calculator shows its workings: which rate it applied, which threshold it used, and where a figure is a projection rather than a published rate. Where we have had to derive a future year from announced policy — company car percentages beyond 2026/27, for instance — it is labelled as projected rather than presented as fact.
These are tools for getting to a defensible number quickly, not a substitute for advice. Anything with real money riding on it should go past your accountant, and where a calculation depends on a judgement rather than a rate — whether an apprentice qualifies for a lower band, whether a contract’s interest clause is a substantial remedy — the tool says so rather than guessing on your behalf.
Something missing? We are building these in the order readers ask for them. Business rates and relief, the VAT registration threshold, and redundancy cost are the three most requested so far. Tell us what you would use at jb@smartsme.co.uk.