The tax bill is not a surprise, it is just late. Put in what you invoice, what it costs you and the share of profit you expect to owe, and see what to move into a separate pot from every payment that lands. Free, and no signup needed.
Is this you?
If two or more sound familiar, the problem is not the tax, it is that the money was never separated from the rest. The calculator below works out how much to move and when.
These boxes are filled in with an example business, not a real one. Replace each number with your own.
The costs of running the business, not what you pay yourself.
Your figure, not ours. If you do not know it, ask your accountant before relying on this.
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Everything is worked out in your browser. Nothing is sent anywhere unless you choose to email the result to yourself. This is a budgeting aid, not a tax calculation, and it is not a substitute for advice from an accountant who knows your situation.
Three things make tax feel like an ambush when it is really just late.
It is charged on profit, and paid out of whatever is left. Most people set aside a share of what they invoice, if they set anything aside at all. But the bill follows profit, and profit moves with your costs. A good month with high costs owes less than it looks, and a lean month with low costs owes more.
The money arrives long before the bill. By the time it is due you have had that money in your account for months, and money in an account gets spent. It never felt like the tax office's money because it was sitting in the same place as yours.
Nothing tells you where you stand until the end. If you do not know your profit as the year goes along, you cannot know what you owe until someone works it out for you, and by then it is due.
Only about 1 in 5 invoicing businesses (25 of 112) records any expenses alongside its invoices.
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).
That is the heart of it. If your costs are not recorded anywhere, your profit is a guess, and anything you set aside against a guess is a guess too. The businesses that get caught out are rarely the ones earning least. They are the ones who could not see the number coming.
It works out the tax on a typical month's profit, then expresses that as a share of what you invoice, because a share of each payment is the only instruction you can actually follow when money lands.
monthly profit = invoiced - costs
tax each month = profit x the share you expect to owe
share to move = tax each month / invoiced
due this period = tax each month x months in the period
you should have = tax each month x months already gone
The share to move is the number worth writing on the wall. In the example, a business invoicing $8,000 with $3,000 of costs and expecting to owe 28% of profit needs to move 17.5% of every payment, not 28%. Moving 28% of everything would starve the business, and moving nothing is how the bill becomes a crisis.
Work out the gap, divide it by the months left before the bill, and add that to what you are already moving. If the catch-up figure is larger than the business can carry, that is worth knowing now rather than the week before it is due: it is a conversation with your accountant, and in many places a payment plan is possible if you ask before the deadline rather than after it.
Do not let being behind stop you starting. Setting aside the right share from today still shrinks the problem, even if it does not close it.
If the tax pot keeps getting raided, the cause is usually cash timing rather than the tax. The cash gap check shows when your money actually lands against when your bills fall due.
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