One client pays most of the bills, and when they pay late, or go quiet, the whole month wobbles. Put in your own numbers to see how much of your income rests on them, the gap they would leave, and how long your cash would cover it. Free, and no signup needed.
Is this you?
If two or more sound familiar, one client is probably carrying more of your business than is safe. The check below puts a number on it.
These boxes are filled in with an example business, not a real one. Replace each number with your own.
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A planning check built only from the numbers you enter. It assumes your outgoings stay the same if the client leaves, which is the cautious reading. Treat it as a guide, not a forecast, and not financial advice.
Nobody plans it. A good client sends more work, the work is steady, and saying yes to them is easier than finding someone new. Over a year or two they grow from one client among many to the one that pays the rent. It feels like security, so there is little pressure to change anything.
None of this means a big client is a bad client. Most are good ones. The risk is not the client, it is having no plan for the day they pay late, cut back or leave.
From our invoice data: In 45% of small businesses, one client accounts for half or more of a year's billing (58 businesses).
Source: Billbooks invoice data, 8,483 invoices from 112 small businesses, September 2024 to September 2026 (aggregate only, figures shown only where 25+ businesses contribute). See the invoice payment study
Most of the cost arrives quietly, long before anyone leaves. When one client pays late, you cannot pay your own suppliers on time, so their delay becomes yours. You accept rush work and thinner prices because turning them down feels too risky. Then there is the day it does end: a new manager, a merger, a budget cut, or the work moving in house. The income drops at once, while rent, wages and software carry on at the old level. If you ever want to sell the business, a buyer will ask about it too, because a business that rests on one client is worth less to someone else.
Yearly figures are divided by 12 so everything is compared month by month. The check then asks one question: if the biggest client stopped tomorrow and nothing else changed, what would be left?
Share = biggest client's billing / all billing Monthly income without them = all billing per month - their billing per month Monthly shortfall = monthly outgoings - income without them (0 if income still covers outgoings) Months of cover = cash in the bank / monthly shortfall New billing needed = their billing per month / chosen share - all billing per monthThe bands are a rule of thumb, not an accounting standard: under 25% is low exposure, 25% to 49% is worth watching, and 50% or more means one client is carrying the business. A business with long contracts and a notice period can live with a higher share than one that works job to job.
The check is cautious on purpose. When a client leaves, some costs usually go with them, such as materials or a subcontractor you only used for their work. If that applies to you, take those costs out of monthly outgoings and run it again.
List last year's billing by client, largest first. It takes one export or one evening with your invoices, and it tells you exactly how exposed you are.
A clause asking for 30, 60 or 90 days' notice to end the work turns a sudden loss into a planned one. Raise it at the next renewal or price review.
Set aside a fixed slice of every payment from your biggest client until your cash would cover the shortfall for several months.
Your second and third biggest clients already trust you. Asking what else they need is the quickest route to new billing, faster than finding strangers.
The fix is a habit rather than a single decision: look at your billing by client every quarter, set a share at which you start actively looking for new work, put a notice period in every ongoing agreement, and keep a cash reserve sized to the gap your biggest client would leave. A spreadsheet is enough to do all of it. If you invoice in Billbooks, its invoices report filters by client and date range, so the figures for this check take a couple of minutes.
Put in what you have and what you spend each month to see your runway, with or without that client's income.
Work out your cash runwayFree · No signup
Does that big client also pay late? The late payment cost calculator puts a yearly figure on it. Busy, but the bank balance still sinks? Try the cash gap check.
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