Unit economics: the three numbers that tell you if you're actually making money

Unit economics has a reputation as a startup metric — something venture investors ask about. That framing has done real damage, because the underlying question is one every business needs answered: does one more customer make me better off or worse off?

You can be profitable in aggregate and still be losing money on a third of your customers. Growth then makes things worse, quietly, while revenue goes up and everyone congratulates each other.

The three numbers

1. What it costs to win a customer

Total sales and marketing spend in a period, divided by customers acquired in that period. Include everything: advertising, the commission, the proportion of your own time spent selling, the tools.

Owners routinely underestimate this by half, usually by leaving out their own effort. If you personally spend two days a week selling, that's a real cost even though it doesn't appear anywhere on the P&L.

2. What a customer is worth

Gross margin per customer per period, multiplied by how long they stay. Note gross margin, not revenue — a customer paying $2,000 a month who costs $1,400 to serve is worth $600 a month to you, not $2,000.

For lifespan, use what actually happened. If your average client relationship has run three years, use three years. Don't use the longest one.

3. How long until you're square

Acquisition cost divided by monthly gross margin. If it costs $6,000 to win a client who contributes $1,000 a month, payback is six months.

This is the number that matters most for cash, and the one most often ignored. A customer who is highly profitable over three years but takes fourteen months to repay acquisition cost is a cash problem right now, however good they look in the lifetime figure.

What good looks like

Rules of thumb, not laws:

• Value to acquisition cost of 3:1 or better. Below that, too much of the customer's worth is consumed winning them. Well above 5:1, you may be under-investing in growth.
• Payback under twelve months. Under six is strong. Beyond eighteen, you are financing your own growth for a long time and need the balance sheet to support it.
• Gross margin stable or improving as you scale. If it erodes as you grow, you're buying revenue by discounting or by serving customers you're not set up to serve.

Cut it by segment or don't bother

This is where the analysis earns its keep. A blended average across the whole business almost always hides the answer.

Cut it by service line, by client size, by acquisition channel, by industry. The typical finding is uncomfortable and useful: referred clients pay back in three months and stay four years; clients from the paid channel pay back in eleven months and leave in eighteen. Both are inside the same average, and only one is worth more of.

Blended unit economics tell you the business is fine. Segmented unit economics tell you what to do on Monday.

The decisions it changes

• Pricing. If payback is too long, a modest price increase usually fixes it faster than cutting acquisition spend.
• Where to spend. Put money into the channel with the shortest payback, not the largest volume.
• Who to fire. Some segments are worth declining. That's easier to act on when you can see the number.
• How fast to grow. Payback period times monthly acquisition spend tells you roughly how much working capital growth will consume.

Start rough

Perfect cost allocation isn't the point and will stop you finishing. Take a quarter, split customers into three or four sensible groups, and work the three numbers for each. The differences between groups will be large enough that precision doesn't change the conclusion.

The unit economics calculator will run it for one segment in a couple of minutes.