Free tool · United Kingdom
United Kingdom CoastFIRE Calculator
Your CoastFIRE number with New State Pension factored in. Slide your inputs and the chart, projection, and monthly retirement income update live.
How to calculate your CoastFIRE number
CoastFIRE is the dollar amount you'd need invested today so that compound growth alone — with zero new contributions — carries your portfolio to your retirement target by your target retirement age. To calculate your CoastFIRE number, work through three steps.
1. Calculate your required portfolio at retirement
Divide your expected annual expenses in retirement by your safe withdrawal rate (the 4% rule is the conventional starting point).
Required at retirement = Annual expenses ÷ Safe withdrawal rate
Example: $50,000 a year ÷ 4% = $1,250,000 needed at retirement. If you expect a public pension (CPP, Social Security, State Pension), subtract its annual value from your expenses first.
2. Calculate your real (inflation-adjusted) return
CoastFIRE math works in today's dollars, so convert your nominal return into a real return using the Fisher equation.
Real return = (1 + Nominal) ÷ (1 + Inflation) − 1
Example: 7% nominal ÷ 2.5% inflation = roughly 4.4% real.
3. Discount your retirement target back to today
Divide the required portfolio at retirement by (1 + real return) raised to the number of years until you retire. That's your CoastFIRE number — what you'd need invested today.
CoastFIRE number = Required at retirement ÷ (1 + Real return)^Years to retirement
Example: $1,250,000 ÷ (1.044)^35 ≈ $283,000. If you have at least $283,000 invested today and you're 35 years from retirement, you can stop contributing — compounding takes you the rest of the way.
How to use this calculator
- 1
Enter your age and target retirement age
Set the sliders for your current age and the age you want to retire. The gap is your runway.
- 2
Set your current portfolio and monthly contribution
Drag the balance and contribution sliders to match what you have invested today and what you're adding each month.
- 3
Tune the assumptions
Adjust expected return, inflation, and safe withdrawal rate. Defaults reflect a balanced equity portfolio.
- 4
Read your CoastFIRE number
The headline shows what you'd need invested today to coast to retirement with zero new contributions, plus how many years until you reach it at your current pace.
Frequently asked questions
- What is CoastFIRE?
- CoastFIRE is the point at which your invested portfolio is large enough that, without any new contributions, compound growth alone will carry it to your retirement number by your target retirement age. After hitting CoastFIRE you no longer need to save for retirement — you can spend what you earn, as long as your portfolio keeps growing.
- How is the CoastFIRE number calculated?
- We start with your annual expenses in retirement, divide by your safe withdrawal rate to get the portfolio you need at retirement, then discount that target back to today using your real (inflation-adjusted) expected return. The result is the dollar amount you'd need invested today to coast to retirement with zero new contributions.
- What return rate should I use?
- A 6–8% nominal return is the conventional assumption for a diversified equity-heavy portfolio over a multi-decade horizon. Pair it with a 2–3% inflation assumption to get a real return in the 4–5% range. Lowering these by even a percentage point materially changes the result — try a few scenarios.
- Is the 4% safe withdrawal rate still valid?
- The 4% rule (Trinity Study) is the conventional starting point for a 30-year retirement with a 60/40 portfolio. Recent research argues for slightly more conservative rates (3.3–3.7%) for longer horizons or worse starting valuations. Adjust the slider to test sensitivity.
- Does this account for taxes or fees?
- No. The projection is a pre-tax, pre-fee model in today's dollars. In practice, withdrawals from taxable accounts incur capital-gains tax, retirement accounts are taxed on withdrawal in many jurisdictions, and management fees compound against you. Treat the result as an optimistic ceiling and stress-test it.
- Are my inputs saved?
- Yes. The calculator stores your last inputs in your browser's local storage, so they'll be there next time you visit. You can also copy a shareable link that encodes your inputs in the URL — the URL takes precedence over saved values when opened.
- How does the State Pension affect my CoastFIRE number in the UK?
- The new State Pension provides a guaranteed weekly income from State Pension age (currently 66, rising to 67 by 2028) to anyone with the required National Insurance contributions. We treat its annual value as an offset to your retirement expenses, reducing the portfolio target and therefore your CoastFIRE number.
- What about ISAs, SIPPs, and workplace pensions?
- The calculator combines all investable assets — Stocks & Shares ISA, SIPP, workplace pension, taxable accounts — into one pool. Withdrawal tax treatment differs (ISA tax-free, SIPP and workplace pensions taxable above the personal allowance), so a complete plan models them separately.