The Slow Lane / Fast Lane Combination
- Difficulty
- Easy
- Time to result
- ~ongoing to results
- Steps
- 6
- Confidence
- —
Mark Tilbury refuses the usual either/or between index-fund saving and entrepreneurship — he ran both lanes at once from his late teens. The slow lane is a fixed ~10% of everything he earned, paid automatically into an index fund inside a tax wrapper and never touched, functioning purely as a psychological and financial safety net. The fast lane is everything else: buying a business, reinvesting profits, and compounding his own skill rather than only the market's return. The point of the slow lane is not to make him rich; it is to make the fast lane survivable, because a founder with an untouchable floor can take business risk without existential fear. Decades later he still has not drawn on it.
Origin
Extracted from Deep Dive with Ali Abdaal
How to run it
- 1
Notice you have sold all your time
Add up every paid hour you work — day job, weekend job, evening teaching. When there are no hours left to sell, your income is capped and no amount of hustle changes it. That ceiling is the trigger to build a second lane.
Pro tip Write the hours down. The trap is invisible until it is on paper.
- 2
Ring-fence roughly 10% of everything you earn
Before lifestyle, before business reinvestment, move about a tenth of income into a broad, low-cost index fund held in the most tax-efficient wrapper available to you (in the UK, an ISA). Start at whatever age you are now, at whatever amount you can sustain.
Pro tip Automate the transfer on payday so it never competes with a spending decision.
- 3
Declare it untouchable
Treat the fund as a safety net, not a war chest. Mark decided on day one he would never touch it, and at 55 still hasn't. The value is the confidence it gives you to take business risk elsewhere.
Watch out Raiding it to plug a business cash-flow hole converts your floor into your risk capital and removes the whole benefit.
- 4
Point everything else at the fast lane
Surplus energy and capital go into the business you control — buying the shop, designing the product, building the audience. This is where the non-linear return lives; the fund will never make you wealthy on its own.
Pro tip Invest in yourself and your own skill first; it is the only asset that raises the ceiling on every future lane.
- 5
Reinvest business profits rather than harvest them
Mark describes himself as a very keen reinvester who takes little out. Profits fund the next container, the next design, the next piece of equipment, compounding inside the business at a rate the market rarely matches.
- 6
Ignore the daily number
You do not check your house price every morning; do not check the fund either. Keep contributing through drawdowns and let the decades of historic average growth do the work in the background.
Pro tip Set a single annual review date and nothing more frequent.
Watch out Selling during a dip is the only way this strategy reliably fails.
In the wild
From around 18, Mark paid roughly 10% of his earnings into an index fund every month and never withdrew a penny. At 20 he took a startup loan, bought a model shop, and poured everything else into the business — later adding design, manufacturing and distribution arms. At 55 the fast lane pays his income and the slow lane sits untouched behind it. He notes he could draw on it or on his pensions today, but has no need to, because other revenue streams cover him.
→ Business income funds the lifestyle while an untouched, decades-compounded fund provides a permanent floor.
Mark drew money out of his investments once, to buy one of his warehouses. It happened to be during the dot-com bubble, roughly a week before it burst. He describes it openly as luck rather than skill — the timing was accidental, not a system. Every other purchase has come from business cash flow rather than from the fund.
→ A single exception that worked by luck, which he does not present as repeatable.
Common mistakes
Waiting for the business to work before investing
People postpone the slow lane until the fast lane pays off, losing the earliest and most valuable compounding years. Mark started at roughly 18, before any business existed, precisely because the amount mattered less than the start date.
Using the safety net as business capital
The fund only does its job if it is genuinely untouchable. Once you treat it as a reserve to be drawn on when trading gets tight, you carry the same fear as a founder with no floor and lose the psychological benefit entirely.
Judging the fund on short-term moves
Checking the balance during a dip triggers selling. Mark's analogy is the house you live in: you do not revalue it daily because you are not selling it. Take the small losses when they come and keep contributing.
From the transcript
“Well, I used a combination of the two. I've always put away approximately 10% of what I earn into an index fund.”
“I always thought from the day I started putting into an index fund, I would never ever touch that money.”
“You are going to be a millionaire if you put a amount of a decent coffee away every day into your index fund.”
From the episode
A Millionaires Masterclass In Business, Side-Hustles and Passive Income - Mark Tilbury
Mark Tilbury