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.

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.

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

How this calculator works

What it calculates: Your Coast FIRE number (the minimum invested today to reach full financial independence without further contributions), your FI number (total pot needed at retirement), projected portfolio growth year by year, and how long it will take to reach Coast FIRE at a given monthly contribution rate.
Key assumptions: Annual growth rate applies to the full invested portfolio
Monthly contributions (if entered) compound at the same rate
Returns and spending figures are in today's money (real terms)
No contributions assumed after reaching Coast FIRE
The maths: FI Number = Annual Spending ÷ SWR
Coast Number = FI Number ÷ (1 + r)ⁿ
Where r is the annual growth rate and n is years to retirement.
When it may not be accurate: Real investment returns vary and are not guaranteed. The calculator does not model tax wrappers (ISA, SIPP, GIA) differently, does not account for inflation on living costs, and assumes constant contributions with no career breaks. Treat results as a planning guide, not a forecast.

Coast FIRE Guide

What is Coast FIRE and how does it work?

Coast FIRE is a milestone in the FIRE (Financial Independence, Retire Early) journey. It is the point at which you have enough money invested that your portfolio will grow on its own to fund your retirement by your target age, without you ever needing to add another penny. Understanding the maths behind it can help you set realistic targets and make smarter decisions about how long to keep saving aggressively.

The FI Number

Your FI number and the safe withdrawal rate

The foundation of any Coast FIRE calculation is your FI number: the total investment pot you need at retirement to fund your spending indefinitely. It is calculated by dividing your target annual spending by your safe withdrawal rate (SWR). If you want to spend £30,000 per year in retirement and use a 4% SWR, your FI number is £750,000.

The 4% rule comes from the Trinity Study, which found that a portfolio of stocks and bonds could sustain a 4% annual withdrawal for at least 30 years in almost all historical scenarios. Many UK FIRE planners use 3.5% for a longer retirement horizon or to account for sequence-of-returns risk. A lower SWR means a larger FI number and a larger Coast number.

Compound Growth

From FI number to Coast number: the power of compound growth

Your Coast FIRE number is simply the present value of your FI number, discounted at your expected growth rate over the years until retirement. If your FI number is £750,000 and retirement is 30 years away, you only need to have about £98,600 invested today for compound growth at 7% to carry you to £750,000 on its own.

This is why time in the market matters so much. Every extra year you can leave money invested roughly halves the amount you need to have saved to Coast. Someone who starts investing at 25 needs a much smaller Coast number than someone starting at 40, even targeting the same retirement pot.

After Coast FIRE

What changes when you reach Coast FIRE

Reaching Coast FIRE does not mean you stop working. You still need to cover your day-to-day living costs. What changes is the pressure to save. Once you are coasting, you no longer need to set aside money for retirement because your existing pot will do the work. Many people use this flexibility to switch to less demanding or lower-paid work, move part-time, or pursue careers they find more meaningful without worrying about retirement savings.

The key risk is sequence of returns: a large market downturn shortly after you stop contributing can delay your projected retirement date. Building in a margin (for example, targeting 110% of your Coast number before stopping contributions) provides a cushion against a poor run of early returns.

Growth Rate

Choosing a realistic growth rate

The calculator defaults to 7% per year, which approximates the long-run real return of a globally diversified equity portfolio. Global equity indices have returned roughly 9–10% nominally over the past century, and after stripping out 2–3% inflation you get a real return in the 7–8% range. This is not guaranteed, and returns vary significantly decade to decade.

If your portfolio is more cautiously invested (bonds, cash, property), use a lower rate: 5% or even 4% for a mixed portfolio. Conversely, if you are investing purely in equities over a very long horizon, 7–8% is a reasonable central estimate. Run the calculator at multiple rates (optimistic, central, conservative) to see a range of outcomes rather than anchoring on a single number.

FIRE Milestones

Coast FIRE, Barista FIRE, and full FIRE compared

Coast FIRE sits between active saving and full financial independence. Full FIRE means you have already reached your FI number and can retire entirely from paid work. Barista FIRE (sometimes called Semi-FIRE) is where your investments cover most of your expenses and you earn just enough from part-time work to cover the gap and ideally employer benefits such as health insurance. Coast FIRE is the earliest milestone: your investments are set but you still need your full income to cover living costs.

For many people, Coast FIRE is the most achievable near-term goal and the one that creates the most immediate change in how work feels. Knowing you no longer need to save for retirement transforms discretionary income from an obligation into a genuine choice.

Sources & methodology

Built and maintained by UK Money Tools, a personal finance resource (not a financial adviser). Last reviewed April 2026. Rates and thresholds come from official UK government publications.

MoneyHelper: Pensions and retirement · Retirement planning guidance from the UK government-backed service
ONS: National life tables · UK life expectancy data for retirement horizon context
FCA: Consumer investments · Investment risk, returns, and consumer protection rules

Figures are estimates only. This is not financial or tax advice. For help with your specific situation, speak to HMRC or a qualified adviser.