Most SME owners have a rough idea of their costs. Very few can tell you — precisely — which are fixed, which are variable, and what happens to their total cost base if any one of them rises. This tool gives you that clarity. Every cost classified. Every scenario modelled. Plain English throughout.
Every cost you enter is classified as fixed, variable, or semi-variable — with a plain-English reason specific to your cost type and UK business context.
Toggle on to set a % change for each cost type. Instantly see the impact on your total cost base, per-type totals, and each individual cost line.
Visual bar chart showing your fixed, variable, and semi-variable split as a proportion of total monthly costs. Instantly reveals where risk and flexibility sit.
Automated insights based on your cost structure — fixed cost burden, variable model risk, semi-variable splits, and break-even floor implications.
A plain-English summary of your cost position with four prioritised management actions — structured like a board-level commercial review.
Download a professional PDF with your complete classification table, sensitivity analysis, cost structure summary, and recommended actions.
Before you can manage your costs, you need to know what type each one is. The classification determines how your costs behave when revenue changes — and that determines your commercial risk.
Fixed costs are paid every month whether you sell one unit or ten thousand. Rent, salaries, loan repayments, insurance, business rates — all fixed. They create your break-even floor: the minimum revenue you must generate before making any profit.
Variable costs only arise when you produce or sell. Stock, packaging, delivery, transaction fees, sales commission — all variable. No activity = no cost. They reduce naturally when trading is slower, which provides commercial flexibility.
Semi-variable costs (also called mixed costs) have a minimum base you always pay, plus an amount that varies with usage. Utilities, phone contracts, and some SaaS tools all behave this way. Splitting them accurately improves your break-even calculation.
The tool is designed to take under five minutes for a complete analysis. Here is how to get the most from it.
Choose from Retail/E-commerce, Service/Consultancy, Manufacturing, Hospitality/Food, Trade/Construction, or Other. This loads a set of relevant default costs for your sector — you can edit, add, or remove any of them.
Work through your bank statement or P&L and enter every cost you pay. Use the monthly amount excluding VAT. The more complete your list, the more accurate and useful the output. Include everything — even small subscriptions add up.
Toggle on the sensitivity feature and set a % change for each cost type. Use this to model specific scenarios — for example, what happens if raw material costs rise 15%, or if you renegotiate your lease and fixed costs fall 8%.
Click Run analysis. Every cost is classified instantly with a plain-English reason. The sensitivity table shows the exact monetary impact of your scenario. Results appear on the right — scroll down to see the full breakdown.
The tool generates management insights based on your specific cost structure — whether your fixed burden is high or low, what your variable costs mean for margin risk, and what actions to prioritise. The executive summary frames these as a commercial brief.
Click PDF Report to generate a professional downloadable document — full classification table, sensitivity analysis if enabled, cost structure summary, and four prioritised management actions. Suitable for sharing with your accountant, board, or business partner.
The sensitivity analysis feature is what separates the subscriber dashboard version from the free tool. It answers the question every business owner faces but rarely models: if this cost increases, what does that actually do to my numbers?
Set the sliders to reflect a real scenario — an expected rent review, an anticipated supplier price increase, a planned headcount reduction, or an energy cost movement. The tool instantly shows the impact on your total cost base and the projected change per cost line. You can then take the fixed cost total directly into the Pricing Modeller to recalculate your break-even and see whether your current price still holds.
This is particularly important in the current UK environment where multiple costs are moving simultaneously. Modelling them in isolation gives a misleading picture — the sensitivity tool lets you apply changes across all three cost types at once to see the combined effect.
A retail business with £2,500/month rent and £290/month utilities models a rent review and energy increase together. Fixed costs rise by £300/month, semi-variable by £58/month.
Total monthly cost impact: +£358A product business with £8,500/month in stock and £1,100/month delivery costs renegotiates supplier terms. Variable costs fall by £756/month — improving margin immediately.
Total monthly saving: −£756Adding a salaried employee increases fixed costs by £3,500/month (plus employer NI). Model this in the tool and then use the Headcount Modeller to calculate the revenue this hire must generate to break even.
Fixed cost increase: +£3,500+Auditing and cancelling underused software subscriptions reduces fixed overheads. A 15% reduction on £380/month software spend saves £57/month — small individually but significant across multiple cuts.
Monthly overhead saving: −£57Every analysis generates a downloadable PDF report — structured like a professional cost review, built from your actual data. Below is an example using indicative retail business figures.
| Cost type | Current | Change | Projected | Impact |
|---|---|---|---|---|
| Fixed | £7,510 | +10% | £8,261 | +£751 |
| Variable | £9,840 | +8% | £10,627 | +£787 |
| Semi-variable | £405 | +5% | £425 | +£20 |
| Total | £17,755 | — | £19,313 | +£1,558 |
It is a common situation: a business owner can tell you their monthly turnover, has a rough sense of their biggest costs, and knows whether they made money last month. What they typically cannot tell you is the precise split between fixed and variable costs, what percentage of their revenue goes to each, or what happens to their total cost base if any one input changes.
This gap creates real commercial problems. Without knowing your fixed cost base precisely, you cannot calculate your accurate break-even point. Without knowing your variable costs per unit, you cannot price correctly. And without modelling sensitivity, you are making strategic decisions — whether to hire, invest, expand, or hold back — on incomplete information.
Your total fixed costs define the revenue floor beneath your profitability. Every pound of revenue below that floor generates a loss. Every pound above it generates a contribution toward profit at your variable margin rate. This is why fixed cost classification matters: getting it wrong by even 15–20% can mean your break-even calculation is materially inaccurate, and your pricing decisions are built on a false foundation.
Semi-variable costs trip up more SME owners than either fixed or variable costs. The reason is that they look like fixed costs — they appear every month as a regular line in your accounts — but they behave partly like variable costs because part of the charge scales with usage.
Utilities are the most common example. Your electricity bill has a fixed standing charge that you always pay, plus a consumption element that rises when you are operating more intensively. If you treat the whole bill as fixed, you underestimate how much your energy cost rises during peak production. If you treat it as variable, you overestimate your fixed cost base. The correct approach — splitting the fixed floor from the variable element — gives you the most accurate commercial picture.
The sensitivity feature is not a forecasting tool — it is a scenario planning tool. Its job is to answer concrete questions: if my supplier increases raw material costs by 12%, what does that do to my total monthly cost base? If I renegotiate my lease and reduce rent by 10%, how does that change my break-even? If I add two members of staff, what fixed cost commitment am I taking on?
These are the questions that drive real commercial decisions. Having the answers in precise numbers — rather than rough estimates — means you are making those decisions with confidence rather than guesswork.
Quick reference for the most common costs in UK small businesses.
Always fixed. Same amount each month regardless of trading activity.
Fixed. Separate from overtime and commission which are variable.
Fixed. Agreed annual premium, divided into monthly payments.
Fixed. Set by your local authority — unchanged by trading performance.
Fixed. Set by your finance agreement regardless of revenue.
Fixed when on a monthly retainer. One-off project fees are variable.
Variable. You buy more as you sell more — total cost scales with output.
Variable. A direct cost per unit — total spend rises with units sold.
Variable. Each order dispatched generates a cost. No orders = no spend.
Variable. Charged as a % of each transaction. No sales = no fees.
Variable. Only arises when a sale is made — scales directly with revenue.
Variable. Calculated on the value of goods imported — rises with volume.
Semi-variable. Fixed standing charge plus variable consumption element.
Semi-variable. Fixed contract minimum plus variable usage above allowance.
Semi-variable where pricing scales with users. Flat-rate tools are fixed.
The Cost Structure Analyser is included in every LumixAI subscription — along with 20+ other live tools, unlimited PDF reports, and the Command Centre. £19.99/month. 7-day free trial. Cancel any time.