Coast FIRE Calculator

Last updated: April 2026

Coast FIRE inputs

Current savings/investmentsCurrent ageTarget retirement ageAnnual expenses in retirementExpected annual return %Inflation rate %Monthly savings contributionUsed to estimate when you reach Coast FIRE if you are not there yet.

Coast FIRE number

£206,664

Your current savings

£100,000

FIRE number at retirement

£750,000

Real return

4.39%

48.4% complete

You need £106,664 more to reach Coast FIRE.

If you save £500/month, you will reach Coast FIRE in 8.5 years at age 43.5.

Once you reach Coast FIRE

Stop making investment contributions

Only earn enough to cover day-to-day expenses

Your portfolio does the rest

Work optional jobs, part-time, or passion projects

What is Coast FIRE?

Coast FIRE is the point where your existing investments are large enough to grow to your full FIRE number by retirement age without any further contributions. You are not fully financially independent yet, but the long-term investing work is already done.

Coast FIRE vs Barista FIRE

Coast FIRE means you can stop investing and simply cover your living costs while your portfolio compounds. Barista FIRE usually means you have enough invested to reduce work, but still need part-time income to cover some expenses or benefits before full retirement.

How to reach Coast FIRE faster

UK investors can accelerate Coast FIRE by using stocks and shares ISAs for flexible tax-free access and SIPPs or workplace pensions for tax relief. Keeping fees low, increasing contributions early, and avoiding lifestyle inflation all make the coast point arrive sooner.

About this calculator

The Coast FIRE Calculator helps estimate whether current investments could grow to a future retirement target without further contributions. It is useful for people considering reduced hours, career changes, lower savings, or knowing the portfolio needed today to coast toward financial independence. Use this expanded guide when you need more than a quick result. It explains the assumptions behind the Coast FIRE Calculator, the records to gather, and the decisions the estimate can support. It is especially useful for people checking whether existing investments can grow to a future independence target without more contributions. The strongest use of the page is scenario comparison: change one input at a time, compare the output, and keep a note of which assumption changed.

Coast FIRE Calculator calculation method

The calculator estimates the future FIRE target from annual expenses and withdrawal rate, converts nominal return and inflation to real return where needed, then discounts the future target back to today over the years until retirement. The calculator result depends on the quality of the inputs and on the rule set or formula selected in the calculator above. For practical use, treat the output as a structured estimate: start with the core inputs, review the main outputs, then test the decision points that matter most to your situation. Key decisions include whether current investments are enough to coast, how retirement age affects the target, how return assumptions change the answer.

FIRE target = annual expenses / withdrawal rate
real return = (1 + nominal return) / (1 + inflation) - 1
Coast FIRE number = future FIRE target / (1 + real return) ^ years
better estimate = accurate inputs + correct rule set + realistic assumptions
scenario difference = revised result - original result

How to use the Coast FIRE Calculator

Gather the main inputs first: annual expenses, withdrawal rate, years to retirement.
Check supporting records such as investment account balances and pension statements before entering final figures.
Enter a realistic base case using current documents, not best-case expectations.
Review the main outputs: future FIRE target, Coast FIRE number, current progress.
Run a conservative case with less favourable timing, rates, costs, or returns.
Compare the result with personal investment records, pension statements, and regulated advice where needed where rules, rates, or reporting duties matter.
Save the inputs and calculation date so you can update the estimate when circumstances change.
Gather the main inputs first: annual expenses, withdrawal rate, years to retirement.
Check supporting records such as investment account balances and pension statements before relying on a final number.
Enter one realistic scenario first, using conservative assumptions where the future is uncertain.
Review the main outputs: future FIRE target, Coast FIRE number, current progress.
Run at least one alternative scenario so you can see which input changes the answer most.
Compare the result with personal investment records, pension statements, and regulated advice where needed or the relevant contract, bill, statement, or professional document.
Keep the calculation date and assumptions with your notes so you can revisit the estimate when rates, rules, or circumstances change.

Worked example

Coast target estimate

Input: Future FIRE target GBP 800,000, 20 years to retirement, real return 4%.

Calculation: Coast number is 800,000 / 1.04^20.

Result: The required portfolio today is about GBP 365,000.

Later retirement scenario

Input: Years to retirement increase from 15 to 25.

Calculation: The target is discounted over more years.

Result: The Coast FIRE number today falls because investments have longer to grow.

Lower return scenario

Input: Real return falls from 5% to 2.5%.

Calculation: The discounting effect weakens.

Result: The required portfolio today rises sharply.

Before you rely on the result

The Coast FIRE Calculator is most useful when it is treated as a structured estimate rather than a final decision. It can organise the arithmetic, but it cannot verify bank data, contracts, tax status, crypto exchange records, funding terms, investor documents, or future market conditions.

Use the result to decide what to check next. For business and tax topics, the supporting documents often matter as much as the headline number.

Input	Why it matters	What to check
annual expenses	This input changes either the calculation amount, the classification, or the scenario result.	Check the period, source document, units, tax year, and whether the value is final or estimated.
withdrawal rate	This input changes either the calculation amount, the classification, or the scenario result.	Check the period, source document, units, tax year, and whether the value is final or estimated.
years to retirement	This input changes either the calculation amount, the classification, or the scenario result.	Check the period, source document, units, tax year, and whether the value is final or estimated.
expected return	This input changes either the calculation amount, the classification, or the scenario result.	Check the period, source document, units, tax year, and whether the value is final or estimated.
inflation rate	This input changes either the calculation amount, the classification, or the scenario result.	Check the period, source document, units, tax year, and whether the value is final or estimated.

How to interpret the output

Read the output as a set of decision signals. A low ratio, high cost, short runway, large tax estimate, or long payback period does not automatically decide the issue, but it tells you which assumption deserves attention first.

future FIRE target: Use this output alongside the other figures. Finance results are easiest to misuse when one attractive number is separated from timing, risk, tax, fees, or cash-flow pressure.
Coast FIRE number: Use this output alongside the other figures. Finance results are easiest to misuse when one attractive number is separated from timing, risk, tax, fees, or cash-flow pressure.
current progress: Use this output alongside the other figures. Finance results are easiest to misuse when one attractive number is separated from timing, risk, tax, fees, or cash-flow pressure.
gap to coast: Use this output alongside the other figures. Finance results are easiest to misuse when one attractive number is separated from timing, risk, tax, fees, or cash-flow pressure.
required contribution: Use this output alongside the other figures. Finance results are easiest to misuse when one attractive number is separated from timing, risk, tax, fees, or cash-flow pressure.

Scenario checks worth running

A single calculation can hide risk. Run a base case, a conservative case, and an upside case. If the result changes dramatically after one small input change, that input is probably the assumption to validate before acting.

Scenario	Change to test	What it shows
Base case	Use current evidence and current terms.	Shows the expected result if nothing material changes.
Conservative case	Use higher costs, slower receipts, lower returns, or less favourable rates.	Shows whether the decision still works with weaker assumptions.
Upside case	Use realistic improvements, not wishful thinking.	Shows the possible benefit if the controllable parts improve.

Records to keep

Finance calculations are easier to defend when you can trace each figure back to a document. This is especially important for tax, investor, lender, payroll, crypto, and pension calculations.

investment account balances: Keep this with the calculation so that the assumptions can be reviewed later. If it is estimated, label it clearly.
pension statements: Keep this with the calculation so that the assumptions can be reviewed later. If it is estimated, label it clearly.
expense plan: Keep this with the calculation so that the assumptions can be reviewed later. If it is estimated, label it clearly.
return assumptions: Keep this with the calculation so that the assumptions can be reviewed later. If it is estimated, label it clearly.
retirement age plan: Keep this with the calculation so that the assumptions can be reviewed later. If it is estimated, label it clearly.

Common mistakes and edge cases

Most mistakes come from mixing periods, using gross and net figures together, ignoring fees, assuming rules are unchanged, or treating projections as guarantees.

Return assumptions dominate the result.: Check this before using the result for borrowing, investing, tax reporting, employment decisions, pricing, or business planning.
Inflation-adjusted and nominal figures must not be mixed.: Check this before using the result for borrowing, investing, tax reporting, employment decisions, pricing, or business planning.
Pension access age can affect whether assets are usable.: Check this before using the result for borrowing, investing, tax reporting, employment decisions, pricing, or business planning.
Coasting does not remove the need for emergency savings.: Check this before using the result for borrowing, investing, tax reporting, employment decisions, pricing, or business planning.

What to check before relying on the result

A useful Coast FIRE Calculator result starts with the same evidence you would use if you were checking the answer manually. The calculator can organise the arithmetic, but it cannot know whether a payslip is final, a bill is estimated, a quote excludes fees, or a personal circumstance has changed since the last statement.

Before making a decision, compare the calculator result with the source document that controls the real outcome. For this topic, that usually means checking personal investment records, pension statements, and regulated advice where needed. If there is a difference between the calculator and an official statement, contract, assessment, or professional advice, treat the official document as the stronger source.

investment account balances: Use this as supporting evidence for the calculation. If it is out of date, estimated, or based on a different period, the calculator output may look precise while still being wrong for the decision.
pension statements: Use this as supporting evidence for the calculation. If it is out of date, estimated, or based on a different period, the calculator output may look precise while still being wrong for the decision.
expense plan: Use this as supporting evidence for the calculation. If it is out of date, estimated, or based on a different period, the calculator output may look precise while still being wrong for the decision.
return assumptions: Use this as supporting evidence for the calculation. If it is out of date, estimated, or based on a different period, the calculator output may look precise while still being wrong for the decision.
retirement age plan: Use this as supporting evidence for the calculation. If it is out of date, estimated, or based on a different period, the calculator output may look precise while still being wrong for the decision.

Inputs that usually change the answer

The most important input is not always the largest number on the form. Sometimes a date, threshold, percentage, eligibility flag, or timing assumption changes the result more than the headline amount. This is why scenario testing is more useful than a single calculation.

Input	Why it matters	What to double-check
annual expenses	It feeds directly into the estimate or changes which rule is applied.	Check the period, units, eligibility, and whether the figure is final or estimated.
withdrawal rate	It feeds directly into the estimate or changes which rule is applied.	Check the period, units, eligibility, and whether the figure is final or estimated.
years to retirement	It feeds directly into the estimate or changes which rule is applied.	Check the period, units, eligibility, and whether the figure is final or estimated.
expected return	It feeds directly into the estimate or changes which rule is applied.	Check the period, units, eligibility, and whether the figure is final or estimated.
inflation rate	It feeds directly into the estimate or changes which rule is applied.	Check the period, units, eligibility, and whether the figure is final or estimated.

How to interpret the output

The output should be read as a decision aid, not just a number. For Coast FIRE Calculator, the useful question is often what the result means for timing, affordability, eligibility, comparison, or next steps.

future FIRE target: Use this output alongside the other results rather than in isolation. A monthly amount, percentage, date, or payback figure can look acceptable until fees, timing, evidence, or eligibility conditions are added.
Coast FIRE number: Use this output alongside the other results rather than in isolation. A monthly amount, percentage, date, or payback figure can look acceptable until fees, timing, evidence, or eligibility conditions are added.
current progress: Use this output alongside the other results rather than in isolation. A monthly amount, percentage, date, or payback figure can look acceptable until fees, timing, evidence, or eligibility conditions are added.
gap to coast: Use this output alongside the other results rather than in isolation. A monthly amount, percentage, date, or payback figure can look acceptable until fees, timing, evidence, or eligibility conditions are added.
required contribution: Use this output alongside the other results rather than in isolation. A monthly amount, percentage, date, or payback figure can look acceptable until fees, timing, evidence, or eligibility conditions are added.

Scenarios worth comparing

A single estimate is a snapshot. A better approach is to save a base case, then adjust one assumption at a time. This shows whether the result is stable or whether a small change in timing, rate, usage, income, or cost creates a very different answer.

Scenario	Change one assumption	What the comparison shows
Base case	Use the best current evidence.	Shows the result you would expect if nothing important changes.
Conservative case	Use lower income, higher cost, slower growth, or less favourable timing.	Shows whether the decision still works with less optimistic assumptions.
Improved case	Use the realistic upside, such as lower cost, better rate, higher usage, or stronger evidence.	Shows the potential benefit without treating it as guaranteed.

Common mistakes and edge cases

Most errors come from using the right formula with the wrong assumption. Dates can be counted differently, rates can change, official thresholds can move, and real bills or contracts often include conditions that a simple calculator cannot infer automatically.

Return assumptions dominate the result.: Check this point before using the estimate for a payment, claim, purchase, application, employment decision, or health-related decision.
Inflation-adjusted and nominal figures must not be mixed.: Check this point before using the estimate for a payment, claim, purchase, application, employment decision, or health-related decision.
Pension access age can affect whether assets are usable.: Check this point before using the estimate for a payment, claim, purchase, application, employment decision, or health-related decision.
Coasting does not remove the need for emergency savings.: Check this point before using the estimate for a payment, claim, purchase, application, employment decision, or health-related decision.

Next steps after calculating

Once you have a result, write down the key assumptions and compare them with personal investment records, pension statements, and regulated advice where needed. If the number affects a deadline, tax return, benefit claim, employment issue, medical question, finance agreement, or major purchase, use the calculator as preparation for a more formal check.

For lower-stakes use, the next step may simply be comparing two or three scenarios. For higher-stakes use, the next step should be checking the official guidance, speaking to the relevant organisation, or getting qualified advice before acting.

Important edge cases

Return assumptions dominate the result.
Inflation-adjusted and nominal figures must not be mixed.
Pension access age can affect whether assets are usable.
Coasting does not remove the need for emergency savings.

Limitations and advice boundary

This guide is for general information only and is not financial advice. Tax rules, lender rules, market prices, pension rules, cryptoasset values, and business conditions can change. The calculator is for education and planning, not personalised advice. This guide is for general information only and is not financial advice. The calculator is designed to support understanding and planning, but it cannot verify documents, predict future rule changes, or account for every exception. Use it as an estimate and check the official source before acting where the result matters.

Check personal investment records, pension statements, and regulated advice where needed where the result affects tax, payroll, borrowing, reporting, or a binding commercial decision.
Do not rely on a single scenario where rates, dates, fees, valuations, income, or costs may change.
Keep the records used for the inputs so the calculation can be updated or explained later.
Check personal investment records, pension statements, and regulated advice where needed for current rules, rates, definitions, and eligibility where relevant.
Do not rely on a single scenario where income, costs, dates, rates, usage, or health circumstances may change.
Keep records of the inputs used so that the estimate can be reviewed later.

Frequently asked questions

Is the Coast FIRE Calculator result guaranteed?

No. It is an estimate based on the inputs and calculator assumptions. Real outcomes can change because of tax rules, contracts, lender decisions, market prices, or business performance.

Should I use gross or net figures?

Use the figure requested by the calculator. Mixing gross and net values is one of the fastest ways to distort a finance result.

When should I get professional advice?

Get qualified advice where the result affects tax filing, legal obligations, employment status, investment decisions, lending, insolvency risk, or a major purchase.

What is Coast FIRE?

It means having enough invested today that, with growth, it may reach a retirement target without more contributions.

Does Coast FIRE mean I can stop working?

Not usually. You still need income to cover current living costs.

Should inflation be included?

Yes. Use real returns or consistently inflation-adjust all figures.

Can pensions count?

They can, but access age and tax treatment need planning.

Is the result guaranteed?

No. Investment returns and spending needs can change.

Related calculators

FIRE Number Calculator
Financial Independence Age Calculator
Savings Rate Calculator
Compound Interest Calculator

What does this mean?

This calculator is designed to help you understand the likely number before you make a decision or start an application.

Your result should be checked against official UK guidance, especially if your circumstances include dependants, exemptions, prior leave, or a complex immigration history.

Treat the figure as a planning tool rather than legal advice. Where the answer affects an application deadline or major payment, speak to an authorised adviser.

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