FI Number Calculator

Find the exact portfolio size you need to be financially independent - and how long it will take to get there.

Your numbers

Annual expenses in retirement

How much you expect to spend each year in retirement, including housing, bills, food, and leisure. Exclude mortgage if it will be paid off.

Current invested portfolio (ISAs, SIPPs, GIAs)

The total value of all your invested assets today. Include ISAs, pensions (SIPPs), and general investment accounts. Exclude property, cash savings, and emergency funds.

Annual savings / contributions

How much you add to your investments each year, including pension contributions (employee + employer) and ISA deposits.

Expected annual return (7%)

0%15%

The nominal (before inflation) return you expect. A global equity tracker has historically returned 7-10% per year.

Inflation rate (2.5%)

0%8%

The Bank of England targets 2%. Higher inflation means your money buys less each year, so you need a larger pot.

Real return: 4.4% · All figures in today's money.

What happens to my data?

All calculations run in your browser. Nothing is sent to our servers. Copy the link to share.

Your FI number

£625,000

Based on £25,000/year at a 4% withdrawal rate

Timeline to FI

years

Age 61

target retirement age

Portfolio progress

Current: £0Target: £625,000

£625,000 still to go

Portfolio projection

How your savings rate affects the timeline

Saving more shortens your path to FI - often faster than chasing higher returns.

Annual savings	Monthly	Years to FI	Retire at
£5,000	£417	44	Age 74
£7,500	£625	36	Age 66
£10,000 current	£833	31	Age 61
£15,000	£1,250	25	Age 55
£20,000	£1,667	21	Age 51

Want to understand the maths?

Read: The Ransom Price - Calculating Your Financial Independence Number

The article behind the calculator. How the 4% rule works and why it matters.

Year-by-year breakdown

Embed this calculator on your site

Paste this snippet wherever you'd like the calculator to appear. Free to use, no account required, attribution preserved.

<iframe
  src="https://freedomisntfree.co.uk/tools/fi-number-calculator?embed=1"
  width="100%"
  height="780"
  style="border: 1px solid #e5e7eb; border-radius: 12px; max-width: 720px;"
  loading="lazy"
  title="Freedom Isn't Free calculator"
  referrerpolicy="no-referrer-when-downgrade"
></iframe>

The iframe auto-resizes to fit content if your page listens for fif-embed-resize postMessage events.

What is your FI number?

Your FI number (financial independence number) is the size of the invested portfolio you need before your investment returns can cover your living costs indefinitely. Hit that number and a salary becomes optional. Anything you earn from work after that point is on your terms, not because the next mortgage payment depends on it.

The standard formula is the Rule of 25:

FI number = annual expenses x 25

That multiplier is just the inverse of a 4% safe withdrawal rate. £30,000 of annual expenses gives you a target of £750,000. £40,000 gives you £1,000,000. The calculator above lets you change the withdrawal rate (down to 3.25% if you want a more conservative target, up to 5% if you're willing to accept more sequence-of-returns risk).

Where the 4% rule comes from

The 4% figure originates with the 1994 Trinity Study (Bengen) and follow-on research that tested historic 30-year retirement windows in the US market. A portfolio split between equities and bonds, drawing down 4% in year one and adjusting that pound figure for inflation each year afterwards, survived almost every historic 30-year window without running out of money.

Two caveats worth knowing. The first: the original study was for a 30-year retirement, so anyone retiring in their forties is planning for a 50-year drawdown where 3.25% to 3.5% is a safer assumption. The second: the data is US-centric. UK and global investors who hold a global tracker may want to be slightly more conservative because UK equity returns have historically lagged the US, and currency exposure adds another layer of variance.

How your savings rate moves the finish line

The single biggest lever on your timeline to FI is your savings rate: what percentage of your take-home pay you put into investments. It matters more than return assumptions, more than tax wrappers, more than fund selection. The reason it compounds twice: a higher savings rate sends more money into the portfolio AND reduces the expenses that portfolio has to cover, which lowers your FI number at the same time.

Savings rate (% of take-home)	Years to FI from zero
10%	51
20%	37
30%	28
40%	22
50%	17
60%	12.5
70%	8.5
80%	5.5

Assumes 5% real return and starting from zero. The relationship is not linear. The first ten percentage points of savings rate (10% to 20%) cut 14 years off the timeline. The last ten (70% to 80%) cut three. The biggest gains come from getting your savings rate above 30%, which is where the maths starts to bend dramatically in your favour. Most UK workers default-save 5% to 8% into a workplace pension and treat that as their savings rate. It isn't enough on its own.

Worked examples

£30,000 annual expenses, 30 years old, £50,000 portfolio

FI number at 4% withdrawal rate: £750,000
Saving £1,000/month at 5% real return: roughly 26 years to FI
Saving £2,000/month at the same rate: roughly 16 years
Doubling the savings rate cuts the timeline by 10 years.

£40,000 expenses, 45 years old, £200,000 portfolio, State Pension £12,000 at 67

FI number before State Pension: £1,000,000
Portfolio need from age 67: only £28,000/year, so £700,000 at 4%
The State Pension acts like a £300,000 phantom portfolio. Plug it into the calculator's State Pension field to see the two-phase number.

£25,000 expenses, retire at 40, no State Pension yet

4% rule says £625,000. But you're planning a 50-year drawdown, not 30.
Drop the withdrawal rate to 3.25%: target becomes £769,000.
Early retirees pay a roughly 25% premium on their FI number for the extra decades.

UK-specific adjustments

Two features of the UK system change the maths meaningfully and the calculator handles both.

State Pension bridging

The full new State Pension pays around £12,000 a year and kicks in from age 66, rising to 67 by 2028 and likely 68 later. If you've paid 35 qualifying years of National Insurance you get the full amount. If you stop working early you can voluntarily top up gaps for the years you'd otherwise miss.

Once it starts, the State Pension reduces what your portfolio has to cover. Your FI number effectively splits into two phases: a higher pre-State-Pension phase, then a smaller post-State-Pension phase. The opinion frame matters here too. The State Pension is one of the few financial benefits that working people get back from the system at roughly the rate they paid in, and it tilts your maths in your favour. Use the calculator's State Pension field to factor it in properly.

ISA, SIPP and GIA sequencing

UK investors have access to two genuinely powerful tax-advantaged wrappers, and a third unwrapped account for everything that doesn't fit. The order you draw from them in retirement changes how much portfolio you actually need.

SIPP: upfront tax relief (20%, 40% or 45% depending on your band) and tax-free growth. Access from age 57 from April 2028. Withdrawals taxed as income, with a 25% tax-free lump sum.
Stocks and shares ISA: no upfront relief, but withdrawals are completely tax-free with no age restriction.
GIA: no wrapper benefit, but no access restrictions or contribution caps either. Subject to capital gains and dividend tax above the annual allowances.

A common early-retirement sequence is to live off ISA and GIA balances first to keep taxable income low, then switch to SIPP withdrawals from pension access age. The calculator's wrapper mode lets you split your portfolio across the three and see the post-tax number you'd actually have to spend. If you want to push the optimisation further, the ISA vs SIPP calculator compares the two head-to-head for a given marginal tax rate.

Frequently asked questions

How do you calculate your FI number?

Multiply your expected annual expenses in retirement by 25. The result is the size of the invested portfolio that, drawing down at 4% per year, should cover your spending indefinitely. £30,000 of expenses gives £750,000. £40,000 gives £1,000,000. Use a lower multiplier (around 30x, equivalent to a 3.25% withdrawal rate) if you plan to retire before age 50.

Is the 4% rule safe for early retirees in the UK?

The original 4% research was based on a 30-year US retirement. UK and global investors retiring in their forties or fifties are planning for a 40 to 50-year drawdown, where a more conservative 3.25% to 3.5% withdrawal rate is the prudent choice. The calculator lets you adjust the rate to see how much extra portfolio you need for the safer assumption.

Should I include my house in my FI number?

No. The FI number only counts liquid invested assets you can draw an income from. Your home keeps a roof over your head but does not generate spendable returns unless you sell it or rent rooms. Equity in a paid-off home reduces your annual expenses (no mortgage payment), which is how it shows up in the maths.

How does the State Pension change my FI number?

Once you reach State Pension age (currently 66, rising to 67 by 2028), the full new State Pension pays around £12,000 a year. That reduces what your portfolio has to cover. If your expenses are £30,000 and the State Pension covers £12,000, your portfolio only needs to fund £18,000 a year from that point on. That's a target of £450,000 instead of £750,000. Enter the State Pension amount and age in the calculator to see the two-phase number.

Does the FI number account for inflation?

If you use a real (inflation-adjusted) return rate, the FI number is already in today's pounds and the result reflects purchasing power. A 5% real return means 5% after inflation. The calculator defaults to a 7% nominal return and 2.5% inflation, giving roughly 4.4% real, but both fields are editable.

What is a good savings rate to aim for?

Anything above 30% of take-home pay compresses the timeline dramatically. Below 20% and you are looking at a 35-plus-year journey from zero. The big inflection points are at 30% (28 years), 50% (17 years), and 60% (12.5 years). Most UK workplace pensions default to 5% to 8%, which is not a savings rate on its own; bolt an ISA or SIPP contribution on top of it.