Hundred Summers in Claude and ChatGPT

Use our UK money calculators, and with Premium your own plan, from an AI assistant that supports the Model Context Protocol (MCP), such as Claude or ChatGPT. Ask in your own words; the assistant runs the same engine as this site and shows you the figures, with a link to the calculator. Education, not advice.

The calculators: free, no sign-in

Connector address: https://hundredsummers.co.uk/mcp

All 90 of our free calculators, on UK rules for the current tax year, through two tools:

• List the free UK money calculators (list_calculators): Lists Hundred Summers' free UK personal-finance calculators (pensions, drawdown, annuities, the State Pension, tax, National Insurance, ISAs, inheritance tax, property, mortgages, care, benefits and more), With a topic that narrows it to 12 or fewer, each comes with its input fields, a worked example's values and its web page; without one, names and titles only. Use it to find the calculator for a question before run_calculator.
• Run a UK money calculator (run_calculator): Runs one Hundred Summers calculator on UK rules for the current tax year and returns its results, the inputs used and a link to the calculator's page. Any field left out takes the worked example's value. Education, not advice.

Your plan: Premium

Connector address: https://hundredsummers.co.uk/mcp/plan

When you add it, the assistant sends you to Hundred Summers to sign in and approve it. Your plan stays on your device, so give it to the assistant with your question: in the app, Settings › Storage › Copy my plan for an AI assistant, then paste it in. Or attach an exported plan file (encryption off), or just tell the assistant your figures. Two tools:

• Project my Hundred Summers plan (project_plan): Runs the person's own Hundred Summers plan through the full UK engine (income tax with Scotland's bands, National Insurance, pensions, the State Pension, ISAs, property, care and inheritance tax) year by year to the end of the plan. Returns whether spending is covered every year and when it first falls short, the position at retirement and at the end, lifetime tax, the assumptions used and the figures at five-yearly milestones. Education, not advice.
• Compare what-ifs on my plan (compare_plans): Runs the person's plan and up to 5 variations of it (for example retiring two years later, spending £3,000 a year less, or paying more into a pension) and returns their headline results side by side. Each variation lists only the facts it changes. Education, not advice.
• Earliest retirement age for my plan (find_earliest_retirement_age): Searches the person's plan for the earliest age they could stop work with every year's spending still paid to the end of the plan, on the central projection (the same search as the app's "When could I retire?"). If the planned age falls short, it searches later ages instead. Optional changes (plan facts, as in compare_plans) are applied first. Education, not advice.
• Most I could spend in retirement (max_retirement_spending): Finds the most base retirement spending a year, in today's pounds, that the person's plan could pay every year to the end of the plan on the central projection, with any extra spending in the early years and care costs on top as planned. Optional changes (plan facts, as in compare_plans) are applied first. Education, not advice.

Adding it

• Claude: Settings › Connectors › Add custom connector, then paste the address.
• ChatGPT: add it as a custom connector or app in Settings, where your ChatGPT plan allows custom connectors, then paste the address.
• Other MCP clients: use the address as a remote (Streamable HTTP) server. The plan connector signs in by OAuth.

Try: “How long would a £350,000 pension last if I draw £22,000 a year from 62?”, “What inheritance tax would my estate pay?”, or with your plan attached, “What if I retire two years later, or spend £3,000 a year less?”

What is sent, and what is kept

• Only what you ask the assistant to send. Your plan leaves your device only when you send it.
• Nothing is stored. Figures and plans are worked out in memory and returned; names are removed before a plan runs. We log only which tool was used and how long it took.
• Your assistant’s provider sees what you share with it, under its own terms.
• Disconnect any time in the assistant’s settings. The full detail is in the Privacy Policy.

A step-by-step guide, with what to give the assistant and what to do if an answer comes back empty: Using Hundred Summers in Claude and ChatGPT.

Results are projections on our published assumptions, not recommendations. For personal advice, speak to an FCA-regulated financial adviser.