Coast FIRE explained — how to know when you can stop contributing.
Coast FIRE is the point at which your existing pension and investment pots will compound to your retirement target without another penny of contributions. It's a milestone, not a destination.
- ▸Coast FIRE number = target retirement pot ÷ (1 + growth rate) ^ years to retirement. If your current pot exceeds this number, compound growth alone will get you there.
- ▸A 35-year-old with a £200,000 pot, targeting £800,000 at 60, needs 5% real growth over 25 years. Coast FIRE number: £800,000 ÷ 1.05^25 = £236,000. They're not quite there yet.
- ▸Reaching coast FIRE doesn't mean stopping work — it means the pressure to save aggressively disappears. Earning just enough to cover current expenses becomes viable.
- ▸In the UK, the state pension reduces the retirement target, which in turn lowers the coast FIRE number. Factor it in.
What coast FIRE is
Coast FIRE is a variant of the broader FIRE concept. It answers a specific question: at what point do my existing savings, growing at a reasonable rate, reach my retirement target without any further contributions?
The distinction from full FIRE is important. Full FIRE means having enough to retire immediately. Coast FIRE means having enough invested that compound growth will finish the job — but it still requires earning enough to cover day-to-day expenses until retirement age. No further saving is needed; just no further spending from the pot.
This makes coast FIRE appealing to people who want to reduce work intensity without stopping entirely. A person who reaches coast FIRE at 38 could switch to a lower-paid but more enjoyable career, go part-time, or take extended breaks — knowing their retirement is already funded by the investments they've already made.
The calculation: pot × (1 + r)^years = target
The formula is a rearrangement of the compound growth equation. To find the coast FIRE number — the minimum pot needed today — divide the target retirement pot by the growth factor:
Coast FIRE number = Target ÷ (1 + r)^n
Where r is the expected annual real return (after inflation) and n is the number of years until the target retirement age.
Worked example: a 35-year-old targeting £800,000 at age 60 with an assumed 5% real return.
- n = 25 years
- Growth factor = 1.05^25 = 3.386
- Coast FIRE number = £800,000 ÷ 3.386 = £236,236
If their current pot is £236,236 or more, they have reached coast FIRE. If it's £180,000, they need another £56,000 of contributions (plus growth on those contributions) before they can coast.
The coast FIRE calculator runs this calculation with adjustable inputs for target pot, expected return, and years to retirement.
Why this is powerful: stop contributing but keep working
The psychological shift at coast FIRE is significant. Before it, every pound of income must be split between living expenses and retirement saving. After it, every pound of income only needs to cover current spending. The savings rate can drop to zero.
This opens up options that aggressive savers often lack. Career changes, sabbaticals, starting a business with lower initial income, moving to a lower-cost area — all become more feasible when retirement funding is no longer a constraint.
The trade-off is that coast FIRE depends entirely on investment returns materialising over the remaining years. A prolonged market downturn in the years after reaching coast FIRE could push the target out of reach. There is no margin of safety built into the number unless you deliberately add one — for instance, by targeting a pot 10–20% above your actual need.
The pension growth calculator can model different growth scenarios to stress-test how sensitive your coast FIRE number is to return assumptions.
Coast FIRE in the UK vs the US
Most coast FIRE content originates from the US, and the UK context differs in three material ways.
State pension reduces the target. The full new state pension is £11,502 per year (2025/26). For a couple, that is £23,004 of guaranteed, inflation-linked income from state pension age. This income reduces the amount a private pension pot needs to generate. If a single person needs £25,000 per year in retirement and the state pension covers £11,500, the private pot only needs to generate £13,500 — cutting the required pot (at a 4% withdrawal rate) from £625,000 to £337,500. That nearly halves the coast FIRE number.
No healthcare cost cliff. In the US, early retirees face the prospect of funding health insurance until Medicare eligibility at 65 — a cost that can exceed $20,000 per year for a family. The NHS eliminates this. UK coast FIRE calculations do not need a healthcare buffer.
Pension access age creates a timing constraint. US retirement accounts (401k, IRA) have their own access restrictions, but the UK's pension access age (57 from 2028) means coast FIRE in a pension wrapper only helps from that age onwards. ISA and taxable investments coast freely — they can be accessed at any age. A UK-specific coast FIRE calculation needs to account for which accounts the money sits in, not just the total.
The FIRE calculator incorporates state pension offsets and access age constraints for UK-specific modelling.
- ▸The full new state pension for 2025/26 is £11,502.40 per year. For a couple both receiving full state pension, that is £23,004.80 of inflation-linked income. [Gov.uk]
- ▸UK equities have returned approximately 5% per year in real terms (after inflation) over the long run, though returns vary significantly over shorter periods. [Barclays Equity Gilt Study]
- •Coast FIRE assumes a constant real return over the remaining years. Actual returns are volatile, and sequence of returns matters.
- •Reaching coast FIRE does not account for future spending changes — children, care costs, housing moves.
- •The state pension age and amount are subject to change by future legislation.
This is factual information, not financial advice. If you're unsure what's right for your situation, speak to an FCA-regulated financial adviser.