Retirement Income Calculator: FIRE Number & Pension Gap

The 4% Rule (Trinity Study)

The foundation of modern retirement planning is the Safe Withdrawal Rate (SWR)**. The landmark Trinity Study (1998, updated 2011) found that a **4% annual withdrawal from a diversified portfolio (50–75% equities) has historically survived 30-year retirements with ~95% probability.

Your FIRE number = Annual Expenses × 25

If you spend £30,000 per year, you need £750,000 to retire safely under the 4% rule.

📊 Safe Withdrawal Rate by Retirement Length

Note: For early retirement (40+ year horizon), consider a 3–3.5% withdrawal rate for greater security.

Sequence of Returns Risk

The greatest threat to retirement is *when* market crashes happen, not just how bad they are.

A 30% crash in Year 1 of retirement is catastrophic compared to the same crash in Year 15. Why? Because early withdrawals during a crash sell shares at depressed prices, permanently reducing the portfolio's recovery capacity.

Protection strategies:

• Maintain 2–3 years of expenses in cash/bonds as a buffer
• Use a flexible withdrawal strategy (reduce spending in down years)
• Consider annuities for baseline income coverage

The Pension Gap

The pension gap = Your required monthly income − Your expected state/employer pension.

In the UK, the full State Pension (2024) is approximately £11,500/year (~£960/month). If you need £2,500/month, your gap is £1,540/month — and your portfolio must fund this for 20–30 years.

Inflation: The Silent Wealth Destroyer

At 3% inflation, your purchasing power halves every ~24 years. A £30,000 annual lifestyle today costs £60,000 in 2048. Always plan in real (inflation-adjusted) terms, not nominal.

Frequently Asked Questions

Q: What is the FIRE movement? A: Financial Independence, Retire Early. FIRE practitioners aggressively save 50–70% of income to retire in their 30s–40s. The math is simple: savings rate determines retirement timeline, not income.

Q: Should I include the State Pension in my calculations? A: Yes, but conservatively. The State Pension is subject to government policy changes. Use it as a supplementary income, not your primary retirement plan.

What is a Retirement Income Calculator?

A retirement income calculator estimates how much monthly or annual income your accumulated savings and pension funds can reliably generate throughout retirement — without depleting the portfolio before your planning horizon ends.

The calculation has three inputs: 1. Portfolio size — the total invested assets at retirement 2. Withdrawal rate — the percentage drawn annually (4% is the research-backed baseline for 30-year retirements) 3. Retirement duration — how many years the income must last

Example:** A £500,000 portfolio at a 4% withdrawal rate generates **£20,000/year (£1,667/month)** in sustainable retirement income. Add the UK State Pension (≈£11,500/year in 2024) and the total retirement income is approximately **£31,500/year.

How Much Retirement Income Do I Need in the UK?

Research from Which? (2023) estimates UK retirement income needs by lifestyle:

The State Pension (£11,500/yr for full entitlement) covers essential living for a single person — but leaves a significant pension gap for any higher standard of living. The portfolio size required to bridge that gap at 4% SWR:

* Comfortable single (£31,300 total) − State Pension (£11,500) = £19,800 gap → requires £495,000 invested * Comfortable couple (£43,100 total) − 2× State Pension (£23,000) = £20,100 gap → requires £502,500 invested