Margin of Safety: The Number That Matters More Than Break-Even Itself

Break-even tells you the minimum you need to sell. It says nothing about how close you actually are to that line — and that gap is often the more important number.

Two businesses, same profit, very different risk

Take two workshops, both with £5,000/month fixed costs and a £15 contribution margin per unit — break-even at 333 units either way.

Units soldCurrent profitMargin of safety
Workshop A400£1,000/mo16.7%
Workshop B360£400/mo7.5%

Workshop B is still "profitable" — but a 7.5% sales dip erases all of its profit, while Workshop A can absorb more than double that drop and stay in the black. Two businesses that look similarly healthy on a profit-and-loss statement can be standing in completely different places relative to the edge.

Why this gets missed

Profit is a lagging number — it tells you what already happened. Margin of safety is closer to a forward-looking risk gauge: how much room is actually left before a bad month turns into a loss-making one. It's the number worth checking before a big customer is lost, a cost rises, or a slow season hits.

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Frequently Asked Questions

What's a "healthy" margin of safety?+
There's no universal number, but many advisers treat anything under 10-15% as fragile for a business exposed to seasonal or economic swings — the right threshold depends on how volatile your specific sales actually are.
Does margin of safety change with fixed costs?+
Directly — raising fixed costs (e.g. taking on a bigger lease) raises your break-even point and shrinks your margin of safety at the same sales level, even if nothing else about the business changed.