Nobody sets out to build a business around one client. It happens the pleasant way: a good client asks for more work, you say yes because the work is good and the money is reliable, and each yes makes the next one easier. Prospecting quietly stops, because why would you chase strangers when the person you already like keeps sending work?
Then a budget gets cut, or your contact leaves, or the company is acquired — and 60% of your income ends in a two-line email that took them four seconds to send.
Work out what share of the last twelve months’ revenue came from your largest client. Under 25% is comfortable; past 40% their decisions set your income. Fix it by growing everything else, not by firing anyone — and hold more cash while the number is high.
Work out your actual number
Concentration is one division. Take the last twelve months of paid invoices, total them, and total what your largest client paid you. Divide the second by the first.
Use twelve months rather than the last quarter — a single big project distorts anything shorter. Use money that actually arrived, not money you billed, and count a parent company as one client even if it pays you through three departments with three purchase orders.
Then read it roughly like this:
- Under 25% — comfortable. Losing anyone hurts and nothing breaks.
- 25–40% — normal for a solo business. Worth watching, not worth acting on.
- 40–60% — this client’s decisions now set your income. Their reorganisation is your reorganisation.
- Over 60% — you have one client and some side work. Everything below applies urgently.
Do the same for your top three combined. Three clients at 30% each reads as a healthy spread right up until you notice they’re all in the same industry, funded by the same money, and cutting budgets in the same quarter.
The risk isn’t the ending. It’s everything before it
The cliff is the obvious danger, and it’s not the expensive part. Concentration costs you money continuously, long before anyone cancels anything.
You stop being able to say no. The rush job over a weekend, the fourth revision round that was never in scope, the meeting that could have been an email — you absorb all of it, because the alternative is friction with the client who pays your rent. Every one of those yeses is an unbilled discount.
Your rates freeze. Raising prices on a client who represents 15% of your income is a business conversation. Raising them on a client who represents 60% feels like a threat to your livelihood, so you don’t — and you keep last year’s rate for a third year running. If it’s time to have that conversation anyway, there’s a way to do it calmly.
Scope creeps unchallenged. Pushing back on drift costs a little goodwill. When you can’t afford to spend goodwill, the drift just becomes the job.
You stop selling. This is the compounding one. A full pipeline is what makes concentration survivable, and a big anchor client is exactly what makes you neglect it. By the time you need new clients, you’re starting cold — and cold prospecting takes months you no longer have.
There’s also a version of this the tax authorities care about. If you work only for one company, on their hours, with their equipment, under their direction, some jurisdictions will look at that arrangement and see employment rather than contracting — with consequences for both sides. Concentration alone doesn’t create that problem, but it’s a common ingredient.
Reduce the ratio by growing, not cutting
The instinct when the number looks bad is to drop the big client. Almost always wrong. A good anchor client is an asset — predictable, low-friction, and the thing that funds everything else. The goal is to make them a smaller share of a bigger business.
Set a floor for the rest of the year. Decide what proportion of your time is reserved for other clients — even one day a week — and protect it before the anchor client’s work expands to fill it. Work expands to fill the space you leave it.
Prospect on a schedule, not on a feeling. Two hours a week, in the calendar, while things are good. Prospecting done from comfort produces better clients and better rates than prospecting done from panic, and it’s the only version that’s available when you actually need it.
Turn past clients into current ones. The cheapest new client is an old one. Someone you did good work for eighteen months ago is a warmer lead than any stranger, and a short “here’s what I’m working on, is there anything you need?” costs you nothing.
Diversify the shape as well as the names. A retainer alongside project work is a different kind of income, not just a different client. So is anything that doesn’t bill by the hour.
Hold more cash while the number is high. Concentration and buffer trade off against each other. If one client is 60% of your income, three months of expenses is the floor, not the goal — that buffer is what converts losing them from an emergency into a busy quarter.
When high concentration is a decision
Sometimes the number is high and that’s fine. A twelve-month engagement you deliberately took, at a rate that reflects it, with a real notice period in the contract and six months of expenses in the bank, is a considered position. You know the risk, you’ve been paid for taking it, and you’ve bought yourself time to react.
The problem is never the concentration itself. It’s concentration you didn’t notice, at a rate you set when they were one client among many, with no notice period and no cushion. The difference between those two situations is entirely whether you did the division.
Watch the ratio, not just the total
Revenue going up and concentration going up look identical from inside a good month. Both feel like things are working. Only one of them is a business getting sturdier.
Check the number once a quarter, alongside the other few metrics worth tracking. It moves slowly, which is exactly why it’s easy to miss — nobody wakes up to discover their largest client jumped from 30% to 60% overnight. It happens over four quarters of pleasant, reasonable yeses.
Where Billable comes in
You can do this in a spreadsheet once. The reason most people don’t do it twice is that pulling twelve months of payments together by hand is an hour of work that produces one number.
Billable already holds that data, because it’s the same record you build by invoicing and marking things paid. Every invoice is attached to a client, so your paid totals per client, per project and per period are simply there — which client is carrying your year, how the mix has shifted since last quarter, and what your income looks like with the biggest name removed.
It’s free for your first 2 active projects and a flat $19 a month after that — no seats, no tiers, no per-user fees, however many clients you’re spreading the risk across. See where your money actually comes from.