CairnKnow your money will last. Without sharing it.
Cairn projects your income, pensions and ISAs through UK tax and into old age. It runs on your own computer, so your plans never leave it.
Built around how UK money actually works
Tax, pensions and allowances are modelled year by year, so answers reflect your situation rather than a rule of thumb.
Probability, not guesswork
Thousands of simulated futures show the chance your money lasts, the range of what you could spend, and what you might leave behind.
UK tax built in
Income tax for England, Wales and NI or Scotland, National Insurance, the personal allowance taper and capital gains tax.
Pensions done properly
Net pay and relief at source, annual allowance and taper, MPAA, tax-free cash and the lump sum allowance.
Couples
Each person has their own allowances, ages and accounts, with shared spending and a plan for the survivor.
Stress tests and history
Replay a crash before retirement, a lost decade, or real UK market history from 1871 to 2020.
Inheritance tax and care costs
Estimates IHT with nil-rate and residence bands, including pensions entering the estate from April 2027, and can model paid care in later life.
Longevity risk
Instead of assuming one end age, see how your chance of success changes with how long you actually live.
Budget builder
Fill in the usual household costs, from council tax to streaming, and apply them as your spending in one step.
Spending finder
Find the most you can spend each year for a target chance of success, with or without spending guardrails.
From inputs to answers
Enter income, expenses and accounts in plain editable tables, in today's pounds.
Your finances stay on your computer
No sign-up, no cloud account, no usage tracking.
- Local only. It runs on your own machine and opens in your web browser. Nothing about your plan is sent anywhere.
- History and backups. Each save keeps the previous version, and a backup script writes a dated zip of everything.
- Yours to inspect. Plans are plain JSON files you control.
Coming soon
Cairn is not available to download yet. It will run on Windows, macOS and Linux. Want to know when it is ready?
Email info@scpsoft.comFAQ
Is this financial advice?
No. It is a planning tool, and its results are estimates built on assumptions you can change. For decisions about your own circumstances, speak to a regulated financial adviser.
Does it send my data anywhere?
No. It runs locally and saves plans in a folder on your computer. Usage statistics are switched off.
Which tax year does it use?
2026/27 rules for England, Wales and Northern Ireland, or Scotland. Bands are frozen to April 2031 by default and can optionally rise with inflation afterwards.
How accurate is it?
The tax and engine code is checked against hand-calculated cases, and a bookkeeping test confirms income, spending and tax add up on every sample and on randomly generated plans. Those tests check the arithmetic, not whether a rule has been understood correctly, and any model simplifies real life, so treat results as guidance and check anything important against official sources.
Where does the market history come from?
The Backtest tab uses UK equity, government bond and inflation data from the Jordà-Schularick-Taylor Macrohistory Database (1871-2020), licensed under CC BY-NC-SA 4.0 for non-commercial use.
Can an AI assistant use it?
Yes. An optional MCP server lets an AI assistant read, edit and run your plans. It is not needed to use the planner.