Coast FI Calculator
Find out how much you need today to stop saving for retirement — and whether you can bridge the gap to your pension
What is Coast FI?
Coast FI is the amount you need invested today so that, left completely alone, compounding alone carries you to full retirement — no more contributions required. Unlike full FIRE, you can keep working; you just stop needing to save.
If you plan to retire early, reaching that number is not the whole story: if it’s locked in a pension, you may not be able to access it until years later. This calculator works out the separate “bridge fund” you’d need in accessible savings to cover that gap.
What is Coast FI?
Coast FI is the point where you have enough invested that, left completely alone with no further contributions, compounding alone carries you to full financial independence by the time you want to retire. From that point you can stop saving for retirement entirely — you just need to cover your day-to-day living costs until then, however you choose to do that.
It is different from full FIRE (Financial Independence, Retire Early), which asks for enough money to stop working altogether. Coast FI only asks that your existing pot no longer needs feeding — you can still work, just without the pressure to save.
The UK pension bridge problem
Reaching a Coast FI number is not the same as being able to access it. UK private pensions are locked until a set access age — currently 55, rising to 57 from 2028 — so if you want to stop working before that age, the part of your Coast FI number sitting in a pension is out of reach when you need it most.
This calculator splits your Coast FI number into two pots for exactly that reason: a bridge fund, held in ISAs or other accessible accounts, that needs to cover you from the day you stop working until your pension access age; and a pension coast number, which can sit untouched in your pension and simply needs to grow to your full FI number by that same access age.
A worked example: someone planning to stop full-time work at 50, with a pension they can't touch until 57, needs a bridge fund large enough to cover seven years of expenses — even if their total pot, pension included, already looks like “enough”.
How the bridge fund is calculated
The bridge fund is the present value of the withdrawals you'll need to make from it every year between leaving your career job and reaching your pension access age — the same maths used to value an annuity. If you plan to keep a lower-key “coasting job” for a while after leaving your career, its income offsets those withdrawals: the bridge only needs to cover the shortfall between your expenses and that income, and only for as long as the coasting job lasts.
Once the coasting job stops (or if you never planned one), the bridge needs to cover your full expenses until your pension access age. Both stages are combined into a single bridge fund figure, then discounted back to today's money using your expected return.
The assumptions behind these numbers
- Annual expenses and all figures are in today's money, and your expected return is treated as a real (after-inflation) rate — so both sides of the calculation move together automatically
- Pension access age defaults to 57, editable if yours differs
- Withdrawal rate defaults to 4%, the standard FIRE assumption
- Expected real return defaults to 5% a year
- Withdrawals from the bridge fund are assumed to happen at the end of each year (an ordinary annuity)
What this tool doesn’t account for
- The State Pension — an extra layer of security not reflected in these numbers
- Tax on pension withdrawals, including the 25% tax-free lump sum rules
- Sequence-of-returns risk — this assumes a constant real return every year, which markets do not actually deliver
For a simpler projection without the pension bridge, try our Compound Growth Calculator. If you're moving investments into an ISA, our ISA transfer calculator works out the tax cost of doing that.
FAQs
What is Coast FI?
Coast FI is the point where your existing investments, left completely alone with no further contributions, will grow into a full financial independence number by the time you want to retire. From that point you can stop saving for retirement — you just need to cover your living costs until then.
What is the pension bridge, and why does it matter?
UK private pensions are locked until a set access age — currently 55, rising to 57 from 2028. If you want to stop working before that age, the part of your Coast FI number held in a pension is out of reach. This calculator splits your number into a bridge fund (held in ISAs or other accessible accounts, covering you until pension access age) and a pension coast number (which can sit untouched in your pension), so you can see whether your accessible savings specifically are enough — not just your total.
What if I plan to keep working part-time after I quit my career job?
Enter the age you'll leave your career job, the age you'll stop working entirely, and how much your part-time or lower-stress 'coasting job' will bring in. That income offsets what you need to draw from your bridge fund during that period, reducing (or eliminating) the bridge fund requirement for as long as the coasting job lasts.
What withdrawal rate and return rate should I use?
The calculator defaults to a 4% withdrawal rate — the standard 'safe withdrawal rate' from FIRE research — and a 5% real (after-inflation) return. Both are editable. Because the return rate is a real rate and expenses are entered in today's money, the results already account for inflation on both sides without a separate inflation input.
Does this account for tax or the State Pension?
No. This calculator does not model tax on pension withdrawals (including the 25% tax-free lump sum rules) or the State Pension, both of which would reduce what you actually need. It also assumes a constant real return every year, which markets do not deliver in practice. Treat the result as a planning estimate, not a guarantee.