Trying to figure out your “financial independence number” is equal parts maths, dreaming, and mild existential crisis.
The calculators are easy. It’s the life part that’s trickier.
Depending on who you ask (and how much avocado toast you eat), the answer is somewhere between “a few hundred grand” and “you’ll need £2 million and a side hustle selling digital planners.”
Classic.
The Not-So-Sexy Math (That Still Matters)
Here’s the thing: the basic idea behind Financial Independence (FI) is actually pretty straightforward. You save and invest enough money so that the income it generates can cover your living expenses — ideally forever. No more working for a paycheck unless it brings you joy or at least tolerable banter.
In FI circles, there’s a popular rule of thumb called the 4% rule. It’s based on some research from the U.S. (shoutout to the Trinity Study) and says you can probably withdraw 4% of your invested assets each year without running out of money over a 30-year period. Full disclosure this is the shockingly simple math that blew my mind.
So, if your annual expenses are, say, £25,000…
£25,000 ÷ 0.04 = £625,000
That’s your “FI number.”
Except — and here’s the curveball — that number is built on a whole bunch of assumptions. Like:
- Your expenses never go up (cute).
- The markets perform like they did in the past (lol, ok, we will try not to panic at the swings).
- You never have a weird medical bill, a leaky roof, or a sudden craving to live in a cottage in Wales and raise goats.
In real life, things wiggle.
The UK-Specific Bits
The 4% rule comes from U.S. data, so it’s not a perfect fit for us across the pond. The UK has different tax rules, benefits, pensions, and that glorious invention known as the NHS (thank you, truly).
Some folks argue a safer withdrawal rate here might be closer to 3.5%, especially if you’re ultra-cautious or planning for more than 30 years. That would bump the FI number up:
£25,000 ÷ 0.035 = ~£715,000
Yup, a little steeper — but not impossible.
And don’t forget to factor in:
- State pension (currently around age 67)
- Private pensions (can’t touch until 55–57)
- Housing: Are you renting forever? Mortgaged up? Escaping to a van?
All of it shapes the number.
But Here’s the Real Talk…
When I first ran these numbers, I had a spreadsheet called “Escape Plan” and a fantasy about quitting everything and moving to the Scottish Highlands with my books and a slow cooker. (Still not off the table, honestly.)
But what I was really chasing was options. Breathing room. The confidence that comes from knowing, “Hey, I’ve got a buffer.” That’s freedom too — even if you haven’t reached full FI.
And honestly, full FI isn’t the only option. There are flavours. Sub-genres, if you will. Think of it like a choose-your-own-adventure for money nerds:
Lean FIRE
You reach FI on a minimalist lifestyle — small budget, low cost of living, probably not a lot of artisanal cheese. Great if you want freedom now and don’t mind keeping things simple. Read the skinny on lean FIRE.
Fat FIRE
Same idea, but luxe. More spending room, higher target. Probably still using spreadsheets, but now they include spa days and upgraded train tickets. Get your teeth into Fat FIRE here.
Barista FIRE
You’ve got enough invested to cover most of your needs, and then work part-time or do something low-stress to fill in the gaps — maybe literally at a café, maybe not. Take a sip of coffee and read more about barista FIRE.
Coast FIRE
You’ve invested enough early on that you can stop saving entirely and just coast to retirement — your current self is off the hook, and your future self still gets to chill.
FU Money
Not technically FI, but honestly a crowd favourite. It’s just enough saved that you can walk away from a bad boss, a toxic job, or anything that makes you question your life choices. That little financial parachute that says: “Nope.”
These versions remind me that this isn’t some all-or-nothing game. You don’t have to be sipping margaritas on a beach at 35 to call it a win. You can build freedom in layers. In phases. In your own weird, wonderful way.
Leaning Into Lean FIRE (and Topping Up as I Go)
Right now, I’m loosely aiming for Lean FIRE — a version of financial independence that covers a simple, steady life. Not luxurious, not barebones — just enough to feel calm and okay.
I live in a leafy corner of Zone 4 in London, and I’m not trying to become a hermit or vanish into early retirement. I like the idea of staying in the world — just more on my own terms. Mornings with coffee, unhurried time with family, maybe a walk if the weather behaves.
At the moment, I’m planning around a 5% safe withdrawal rate — a bit more relaxed than the usual 4%, but it makes sense for my setup. I want to cover around £12,000 a year from investments, and gently top up the remaining £5,000 or so through flexible, low-pressure work.
I don’t know exactly what that work will be yet. Maybe a bit of freelance writing. Maybe something unexpected. Ideally, it’ll fit around my life — not the other way around.
There’s a kind of calm in knowing I don’t need to rush. The spreadsheet helps, but it’s the space it creates — the option to say “not today” to things that don’t fit — that feels like real progress.
Gentle Questions for the Road:
Financial independence isn’t about some perfect number or magic age. It’s about creating a life with more room to breathe. For me, that’s meant slowing down, building a bit of a buffer, and trusting that I don’t have to figure everything out at once.
Right now, I’m not working some dream part-time job or living off dividends in the south of France. I’m just slowly building a life that has more yeses than no’s — and a bit of margin around the edges.
If you’re exploring your own version of FI, here are a few questions to carry with you:
- What would “enough” look like for you — not in numbers, but in feelings?
- Which version of FI feels most aligned with the life you actually want, not the one you’re told to want?
- If money weren’t the loudest voice in the room, what would you choose to do differently this year?
You don’t have to move to a cabin in the woods or build a six-figure side hustle. Maybe you just want quiet mornings, fewer spreadsheets, or a bit more room to think.
That counts too.
