What if rates, sales or prices change?
Test your business against higher interest rates, a fall in sales and rising costs, one at a time and all together, and see how long your cash would last.
Your answer
Enter your sales, margin, overheads and cash to see what each change would do.
About this calculator
For small business owners who want to know how much room they have if interest rates go up, sales drop or costs climb. It shows each change on its own and all together, for the business and for your home mortgage.
What happens to your answers
We don’t keep them. Your answers go to our server to do the sums and aren’t stored or logged. If you copy a link to your answers, they’re in the link itself, so only share it with people you trust.
How it’s worked out
Today's profit is your sales, less the direct costs at your gross margin, your overheads and the loan interest over the next 12 months. Then we take off Corporation Tax for a company, or income tax and Class 4 National Insurance for a sole trader.
A rate rise changes a variable loan's payment straight away: we work out the new monthly payment on what you owe over the years left. A fixed rate changes when the fix ends, at today's rate plus the rise. Extra interest is a business cost, so part of it comes back as lower tax; extra capital repaid isn't.
A fall in sales takes your direct costs down with it. Rising costs push up your overheads and direct costs with your prices the same. Your cash runway is your cash divided by what you'd lose each month, after tax and loan repayments, so it can run down even while there's still a profit.
The break-even figure is how much further sales could fall, from each case's level, before profit reaches zero, with your overheads and loan interest staying the same.
Worked example
If interest rates rose 1 point, sales fell 20% and costs rose 5% all at once, your business's profit after tax would fall by £61,896 a year, to a loss of £18,788.
2026/27 · limited company · sales £600,000 · 40% gross margin · loan £100,000 at 7% variable · home mortgage
| Today: sales over the next 12 months | £600,000 |
|---|---|
| Today: direct costs (60% of sales, so a 40% gross margin) | − £360,000 |
| Today: overheads | − £180,000 |
| Today: loan interest in the next 12 months (7% on £100,000, £1,980 a month over 60 months) | − £6,452 |
| Today: profit before tax | £53,548 |
| Today: Corporation Tax | − £10,440 |
| Today: profit after tax | £43,108 |
| Today: loan capital repaid (not a cost for tax, but it leaves the bank) | − £17,310 |
| Today: cash change over 12 months | + £25,798 |
| Today: cash runway (£40,000 ÷ no monthly shortfall) | Cash still grows |
| Today: how far sales can fall from here before a loss | 22.3% |
| Rates up 1 point: profit before tax (sales £600,000 − direct costs £360,000 − overheads £180,000 − loan interest £7,388) | £52,612 |
| Rates up 1 point: Corporation Tax | − £10,192 |
| Rates up 1 point: profit after tax, − £688 on today | £42,420 |
| Rates up 1 point: loan payment £2,028 a month from month 1 (was £1,980), so £570 more in the next 12 months | + £48 |
| Rates up 1 point: loan capital repaid (not a cost for tax, but it leaves the bank) | − £16,944 |
| Rates up 1 point: cash change over 12 months | + £25,476 |
| Rates up 1 point: cash runway (£40,000 ÷ no monthly shortfall) | Cash still grows |
| Rates up 1 point: how far sales can fall from here before a loss | 21.9% |
| Sales down 20%: profit before tax (sales £480,000 − direct costs £288,000 − overheads £180,000 − loan interest £6,452) | £5,548 |
| Sales down 20%: Corporation Tax | − £1,054 |
| Sales down 20%: profit after tax, − £38,614 on today | £4,494 |
| Sales down 20%: loan capital repaid (not a cost for tax, but it leaves the bank) | − £17,310 |
| Sales down 20%: cash change over 12 months | − £12,816 |
| Sales down 20%: cash runway (£40,000 ÷ £1,068 a month short) | 37.4 months |
| Sales down 20%: how far sales can fall from here before a loss | 2.8% |
| Costs up 5%: profit before tax (sales £600,000 − direct costs £378,000 − overheads £189,000 − loan interest £6,452) | £26,548 |
| Costs up 5%: Corporation Tax | − £5,044 |
| Costs up 5%: profit after tax, − £21,604 on today | £21,504 |
| Costs up 5%: loan capital repaid (not a cost for tax, but it leaves the bank) | − £17,310 |
| Costs up 5%: cash change over 12 months | + £4,194 |
| Costs up 5%: cash runway (£40,000 ÷ no monthly shortfall) | Cash still grows |
| Costs up 5%: how far sales can fall from here before a loss | 11.9% |
| All together: profit before tax (sales £480,000 − direct costs £302,400 − overheads £189,000 − loan interest £7,388) | − £18,788 |
| All together: Corporation Tax (none on a loss) | − £0 |
| All together: profit after tax, − £61,896 on today | − £18,788 |
| All together: loan payment £2,028 a month from month 1 (was £1,980), so £570 more in the next 12 months | + £48 |
| All together: loan capital repaid (not a cost for tax, but it leaves the bank) | − £16,944 |
| All together: cash change over 12 months | − £35,732 |
| All together: cash runway (£40,000 ÷ £2,978 a month short) | 13.4 months |
| All together: how far sales can fall from here before a loss | Already a loss |
| Your mortgage today: 4.5% on £200,000 over 264 months | £1,195 |
| Rates up 1 point: your mortgage payment from month 9 (£1,305 a month), so £440 more in the next 12 months. Paid from your own money, after tax | + £110 |
Worked out using HMRC's published rates for the 2026/27 tax year (6 April 2026 to 5 April 2027), on a yearly basis.
Questions people ask
Why isn't 'all together' the three results added up?
Because the changes act on each other. With sales down, there are fewer direct costs for the cost rise to push up, so the combined hit is a little smaller than the three on their own added together.
Why does a rate rise cost less in profit than in payments?
Only the interest is a business cost. The higher payment also repays a little less of the loan early on, which hits your cash but not your profit, and the extra interest gets tax relief.
Should I fix my rate or pay off the loan?
We can't advise on borrowing. This shows what each change would do to your figures, so you can talk it through with your lender or with us.
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