How is the Coast FIRE number calculated?

First, your FI Number is calculated: Annual Spending ÷ Safe Withdrawal Rate (typically 4%). This is the total pot you need at retirement. The Coast FIRE Number is then the amount you need today so that, growing at your assumed rate, it reaches your FI Number by retirement. The formula is: FI Number ÷ (1 + growth rate)^years to retirement.

What safe withdrawal rate should I use?

The 4% rule comes from the Trinity Study and suggests withdrawing 4% of your portfolio per year has historically lasted 30+ years. Some people use 3.5% for extra safety, especially if retiring early with a 40–50 year horizon. Others use 3.25% to 3.5% for very early retirement. 4% is a reasonable default for most scenarios.

What investment growth rate should I assume?

UK and global equity markets have historically returned around 7–10% per year in nominal terms, or roughly 5–7% after inflation. A commonly used real (inflation-adjusted) figure is 5–7%. This calculator uses nominal returns by default. If you want to work in real (today's money) terms, reduce the growth rate by your expected inflation rate (e.g., use 4.5% if inflation is 2.5% and markets return 7%).

What's the difference between FIRE and Coast FIRE?

Full FIRE means your portfolio is already large enough to fund your lifestyle without ever working again. Coast FIRE is a milestone along the way: your investments are on track to reach full FIRE by retirement age, but you still need to work (or have some income) to cover today's living costs. Coast FIRE is achievable much earlier and requires a far smaller pot.

Does Coast FIRE work with a pension?

Yes. If your pension pot is on track to fund your retirement, you may already be at Coast FIRE even if you do not think of it that way. Include all invested assets in your current savings figure: workplace pensions, personal pensions (SIPPs), ISAs, and any other invested assets. Cash savings and property equity are usually excluded as they do not compound in the same way.

Retirement & Pensions

Coast FIRE Calculator

Find your Coast FIRE number — the amount you need invested today so your portfolio grows to fund retirement without any further contributions.

Updated June 2026

Your details

Current age

Target retirement age

30 years to retirement

Current invested savings

Pensions, SIPPs, ISAs, and other invested assets

Target annual spending in retirement

FI number = £750,000 (£30,000 ÷ 4%)

Monthly contributions (optional)

Used to estimate when you'll reach Coast FIRE

Annual growth rate

Safe withdrawal rate

Your results

Not yet at Coast FIRE

At £500/month you'll reach Coast FIRE in 29 years (age 59).

FI Number (target pot at retirement): £750,000
Coast FIRE Number (needed today): £98,525
Current invested savings: £25,000
Shortfall to Coast FIRE: £73,525

Progress to Coast FIRE25.4%

You're 25.4% of the way to your Coast FIRE number of £98,525.

Year-by-year projection

Showing portfolio growth vs your Coast FIRE number needed each year , including £500/month contributions

Age	Portfolio value	Coast number needed	Status
30	£25,000	£98,525	Building
31	£32,750	£105,422	Building
32	£41,043	£112,802	Building
33	£49,915	£120,698	Building
34	£59,410	£129,147	Building
35	£69,568	£138,187	Building

What is Coast FIRE?

Coast FIRE is a milestone in the FIRE (Financial Independence, Retire Early) journey. It's the point at which you have enough invested that your portfolio will grow on its own — without any further contributions — to fund your retirement by your target age.

The name comes from the idea that once you hit this number, you can "coast" to financial independence. You still need to earn money to cover your day-to-day living costs, but you no longer need to save aggressively.

The maths

FI Number = Annual Spending ÷ Safe Withdrawal Rate

Coast Number = FI Number ÷ (1 + Growth Rate)^{Years to Retirement}

For example, if you want to spend £30,000 per year in retirement and use a 4% withdrawal rate, your FI Number is £750,000. If retirement is 30 years away and you expect 7% annual growth, your Coast FIRE number is £750,000 ÷ (1.07)³⁰ = approximately £98,600. Reach that number today and you will never need to add another penny.

Frequently asked questions

Sources & methodology

Built and maintained by Tim, a personal finance enthusiast — not a financial adviser. Last reviewed April 2026. Rates and thresholds are sourced from official UK government publications.

The Pensions Regulator — Auto-enrolment — Qualifying earnings and contribution thresholds
GOV.UK — Tax on your private pension — Tax relief rules and annual allowances
HMRC — Pension schemes — Salary sacrifice and pension scheme types

Results are estimates based on the rates and rules in force for the selected tax year. They do not constitute financial or tax advice. For personalised guidance consult HMRC or a qualified adviser.