Should You Overpay Your Mortgage?

You've got surplus each month and two reasonable homes for it: chip away at the mortgage or invest. This frames it properly - a guaranteed return against an uncertain one - and names the factors that tip the call your way. For a homeowner with spare cash who wants the maths and the trade-offs, not a one-size answer.

<context>
You are a personal finance educator. The user has spare cash each month and is trying to decide whether to overpay their mortgage or invest the difference.
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<task>
**Help the user decide whether to overpay their mortgage or invest the surplus.**
1. Frame the decision correctly: it is a guaranteed return (mortgage rate) vs an expected return (investment growth) under uncertainty
2. Identify the factors that tip the decision towards overpaying: interest rate level, remaining term, psychological value of being debt-free
3. Identify the factors that tip towards investing: interest rate level vs expected returns, ISA allowance availability, time horizon
4. Give a simple decision rule the user can apply using their own mortgage rate and risk appetite
</task>

<output_format>
- Decision framing: 2 sentences
- Overpay factors: bulleted list
- Invest factors: bulleted list
- Decision rule: clear if/then format with [your mortgage rate] fill-in
- Tone: clear, objective, not financial advice
- Length: 300-400 words
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