Break-even analysis: fixed costs, contribution margin and the break-even point

Every business has a sales level below which it loses money and above which it starts to make some. That level is the break-even point. Knowing it turns vague worries (“are we selling enough?”) into a number you can track each week, and it tells you how much room you have before a bad month becomes a loss.

Break-even analysis needs only three inputs: your fixed costs, your selling price and your variable cost per unit. This guide shows how to find each one, how to run the calculation, and how to use the result for pricing and planning decisions.

Fixed costs and variable costs

Start by splitting your costs into two groups.

• Fixed costs stay the same over a normal range of activity. Rent, salaried staff, insurance, software subscriptions and loan repayments usually sit here. You pay them whether you sell ten units or a thousand.
• Variable costs rise and fall with each unit sold. Materials, packaging, payment processing fees, delivery and sales commission are typical examples.

Some costs are mixed. A phone contract might have a fixed monthly fee plus usage charges, and a warehouse might charge a base fee plus a fee per order. Split these into their fixed and variable parts rather than forcing them into one group. If you are unsure, ask how the cost would change if sales doubled next month. If it would double too, treat it as variable. If it would barely move, treat it as fixed.

Contribution margin: what each sale adds

Contribution is the money left from a sale after variable costs are paid. It is what each sale contributes towards fixed costs and, once those are covered, towards profit.

• Unit contribution = selling price minus variable cost per unit
• Contribution margin ratio = unit contribution divided by selling price

The ratio tells you how many pence of each pound of sales are available to cover fixed costs. A business with a 60% ratio keeps 60p of every pound after variable costs. A business with a 20% ratio keeps 20p, so it needs far more sales to cover the same overheads.

Contribution is a different measure from gross margin on your profit and loss account. Gross margin usually deducts cost of goods sold only, while contribution deducts every cost that varies with sales, including payment fees, delivery and commission. For break-even work, contribution is the one you want.

The break-even formulas

Once you have fixed costs and unit contribution, the calculation is short.

• Break-even units = fixed costs divided by unit contribution
• Break-even revenue = fixed costs divided by the contribution margin ratio
• Units for a target profit = (fixed costs plus target profit) divided by unit contribution
• Margin of safety = actual or budgeted sales minus break-even sales, often shown as a percentage of actual sales

The logic is simple. Profit equals total contribution minus fixed costs. At break-even, profit is zero, so total contribution must equal fixed costs exactly.

A worked example

An example (illustration only): a small online candle brand sells one product at £24, excluding VAT. Its costs per candle are:

Unit contribution is £24 minus £11, which is £13. The contribution margin ratio is £13 divided by £24, about 54%.

Monthly fixed costs (studio rent, website platform, insurance and a part-time assistant) come to £3,250.

• Break-even units: £3,250 divided by £13 = 250 candles a month
• Break-even revenue: 250 multiplied by £24 = £6,000 a month (the same as £3,250 divided by 0.5417)
• To earn £1,950 profit a month: (£3,250 + £1,950) divided by £13 = 400 candles
• If the brand sells 320 candles, its margin of safety is 70 candles, or about 22% of sales

Now test a decision. The owner considers a permanent 10% discount, cutting the price to £21.60. Payment fees fall slightly to about £0.65, so variable cost becomes about £10.93 and unit contribution drops to about £10.67. Break-even rises to £3,250 divided by £10.67, roughly 305 candles. A 10% price cut needs about 22% more sales just to stand still. This is why break-even analysis is a useful check on any discounting plan.

How to run it on your own business

1. Pick a period. Monthly works for most small businesses because rent and salaries are paid monthly.
2. List every cost from your accounts for a recent normal period and tag each as fixed, variable or mixed. Split the mixed ones.
3. Work out variable cost per unit. If you sell many products, use a weighted average based on your actual sales mix, or work at revenue level using the contribution margin ratio.
4. Calculate unit contribution and the ratio. Check that contribution is positive. If a product’s variable cost exceeds its price, more sales make things worse.
5. Find break-even units and revenue, then compare them with what you actually sell.
6. Test scenarios. Change the price, a supplier cost or the rent and watch the break-even point move. A spreadsheet with the three inputs in separate cells makes this quick.
7. Track it. Recalculate when prices, suppliers or overheads change, not just once a year.

Common mistakes

• Leaving out small variable costs. Payment fees, returns, free delivery and marketplace commission add up. Missing them overstates contribution and understates break-even.
• Using VAT-inclusive prices. If you are VAT registered, the VAT you collect is not yours. Use prices and costs net of VAT.
• Ignoring the founder’s pay. If the business only breaks even because the owner takes no salary, it has not really broken even. Include a realistic wage in fixed costs.
• Assuming the sales mix will hold. A multi-product break-even point assumes the mix stays constant. If customers shift towards a low-contribution product, the break-even point rises.
• Treating break-even as a target. Break-even means zero profit. It is a floor, not a goal.

When to use it and when not to

Break-even analysis works well for pricing decisions, testing a new product or location, deciding whether a fixed-cost commitment such as a new hire or a bigger unit is affordable, and setting a minimum monthly sales figure for the team.

It has limits. It looks only at costs and says nothing about whether customers will buy at a given price, so pair it with demand evidence. It assumes costs behave in straight lines, which holds only within a normal range of activity: rent jumps when you outgrow the unit, and suppliers offer discounts at volume. It also assumes you sell everything you make, so businesses holding a lot of stock should treat the result with care. Finally, break-even is a profit measure, not a cash measure. A business can pass its break-even point and still run out of cash if customers pay slowly or stock ties up money.

Used with those limits in mind, the break-even point is one of the most practical numbers a small business can know. It takes an hour to work out and gives you a clear line to beat each month.