Using Hundred Summers in Claude and ChatGPT
How to add the Hundred Summers connector to Claude or ChatGPT: the free calculators with no sign-in, your own plan with Premium, what to give the assistant so its answer is real, good questions to ask, what is sent and kept, and what to do when an answer comes back empty.
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Hundred Summers works inside AI assistants that support MCP (the Model Context Protocol), such as Claude and ChatGPT. You ask in your own words; the assistant runs the same engine as this site and shows you the figures, with a link to where they came from. There are two connectors: the calculators, free for anyone, and your own plan, for Premium members. The set-up page, with both addresses and the tools each offers, is Hundred Summers in Claude and ChatGPT.
Adding the free calculators
In Claude, open Settings › Connectors › Add custom connector and paste https://hundredsummers.co.uk/mcp. In ChatGPT, add it as a custom connector or app in Settings, where your ChatGPT plan allows custom connectors. No sign-in is needed. Then ask a question a calculator answers, giving your figures: “How long would a £350,000 pension last if I draw £22,000 a year from 62?”, “How much tax would I pay on a £10,000 bonus on a £55,000 salary?” or “What inheritance tax would an estate of £900,000 with a house pay?” The assistant picks one of our free calculators, fills in what you said and shows the answer with a link to the calculator’s page, where you can check it or change the figures.
Connecting your own plan (Premium)
Add a second connector with the address https://hundredsummers.co.uk/mcp/plan. When you press Connect, the assistant sends you to Hundred Summers: sign in, read what connecting means, and press Approve. You are back in the assistant, connected. You can disconnect at any time in the assistant’s own settings.
Your plan lives on your device, not with us, so signing in can’t fetch it: the assistant needs you to give it the plan each time, in one of three ways:
- Copy it (easiest, and the way on a phone). In Hundred Summers, open Settings › Storage and press Copy my plan for an AI assistant, then paste it into the conversation with your question. It copies the plan you have open, without its name or your health answers, and doesn’t change your backup settings.
- Your plan file. Settings › Storage › Export snapshot, then attach the file. It must not be encrypted, so switch Encrypt backup files off for the export and back on afterwards; an encrypted file can’t be read.
- Your figures, in words. If you’d rather not share the file, tell the assistant enough to build a plan: your age, when you want to retire and how long to plan for (to 95 is a sensible default); your salary; what you spend now and expect to spend in retirement; each pension pot’s value and what you and your employer pay in; savings and ISAs; any final-salary pension and when it starts; and your State Pension forecast, or how many years of National Insurance you have.
The more you give, the more the answer means. A plan with no pensions or savings in it says nothing about whether your money lasts, and the connector tells the assistant so, rather than letting it report an empty result as good news.
Good questions to ask
- “Does my money last to 95, and if not, when does it run short?”
- “What if I retire at 60 instead of 62, or at 65?” The assistant can set up to five versions beside your plan as it is.
- “What happens if I spend £3,000 a year less in retirement?”
- “How much will I have at retirement, and what will my estate pay in inheritance tax?”
- “How much tax will I pay over my lifetime?”
For the stress test across 500 simulated markets, goals, couples planning and the rest, the app itself goes further than the connector: the connector runs the year-by-year projection, what-ifs on it, and two searches: the earliest age you could retire with every year's spending paid, and the most you could spend a year in retirement. It also points out inputs worth checking (no State Pension, an income that looks monthly, pension contributions above the annual allowance) and years the plan can't pay for while your pensions are still locked or your home is never used.
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, and we never store it: it is worked out in memory and the result returned, with names removed before it runs. We log only that a tool was used and how long it took. The assistant’s provider (for example Anthropic for Claude, OpenAI for ChatGPT) sees what you share with it, under its own terms. The full detail is in the Privacy Policy.
When an answer looks wrong
- Every year shows £0. The plan the assistant built is missing your figures. Give it the figures listed above, or attach your plan file, and ask it to run again; the connector names any figures it didn’t recognise.
- “I can’t see your plan.” The assistant has nothing to run yet: copy your plan from Settings › Storage and paste it in.
- “The file can’t be read.” It was exported with encryption on. Copy the plan instead, or export it again with encryption off.
- “Part of Premium.” Connecting your own plan needs Premium; the calculators connector is free.
- The figures differ from the app. Check the facts the assistant used against your plan: the answer lists the assumptions and the figures at each milestone, and the app is the authority.
Try the numbers
Free calculators on the same engine, no sign-up, nothing leaves your browser.