Pension Longevity Calculator
Estimate how long your retirement pot could last based on spending, guaranteed income, expected return, and inflation.
Why this calculator matters
One of the hardest retirement questions is simple to ask and surprisingly hard to answer: “Will my money last?” A pension drawdown plan is affected by multiple moving pieces at the same time: your investment return, inflation, guaranteed income, and your withdrawal rate. This calculator helps you combine those assumptions in one place so you can make a more realistic plan.
Think of this as a planning tool, not a prediction engine. Its value is in showing trade-offs clearly. For example, increasing monthly spending by a few hundred pounds can shorten your pension lifespan by years, while reducing spending slightly or delaying larger withdrawals can have the opposite effect.
How the pension duration calculation works
The model runs month-by-month:
- Starts with your pension pot balance.
- Applies your expected monthly investment return.
- Subtracts your monthly draw from the pot.
- Increases that draw over time using inflation.
Your guaranteed monthly income (such as state pension or annuity income) reduces the amount that needs to come from investments. If your guaranteed income fully covers your spending, the draw from the investment pot becomes zero.
Inputs you should choose carefully
1) Expected return
Many retirement plans fail because of return assumptions that are too optimistic. Use a conservative estimate, especially if your portfolio is not fully invested in equities or if you prefer low volatility.
2) Inflation
Inflation quietly increases your required withdrawals every year. Even modest inflation compounds significantly over a 20- to 30-year retirement horizon.
3) Spending level
Your spending target is often the biggest lever. Build your budget from essentials first, then add discretionary spending. You can also stress test by increasing spending assumptions to see what happens in less favorable scenarios.
4) Guaranteed income
Reliable income streams reduce pressure on your investment portfolio and can materially improve sustainability. Include realistic after-tax income figures where possible.
How to make your pension last longer
- Lower early retirement withdrawals: early years matter most due to compounding.
- Keep a spending guardrail: reduce discretionary spending in weak market years.
- Delay large one-time purchases: this preserves principal when sequence risk is highest.
- Review annually: update assumptions for inflation, returns, and real spending behavior.
- Coordinate income sources: state pension timing and annuity options can improve resilience.
Interpreting your result
If your projection runs out before your target age, that does not automatically mean retirement is impossible. It means your current combination of assumptions is fragile. Typical fixes include trimming planned spending, lowering inflation-sensitive expenses, earning part-time income for a few years, or adjusting portfolio strategy.
If your pension appears to last beyond your target age, that is encouraging, but still test downside scenarios: lower returns, higher inflation, or temporarily higher spending due to healthcare or family support needs.
Quick FAQ
Does this include tax?
No. This tool is pre-tax and simplified. For detailed planning, include tax bands, pension withdrawal taxation, and account type sequencing.
Does it model market crashes?
Not directly. It uses a smooth average return. In reality, return order matters. You can approximate stress testing by lowering expected returns and increasing inflation assumptions.
Should I use one scenario only?
No. Run at least three: optimistic, base case, and conservative. Your plan should survive a conservative scenario, not just a best-case one.
Final thought
A strong retirement plan is not about guessing one perfect number. It is about building flexibility. Use this calculator regularly, keep your assumptions honest, and adjust early when the numbers change.