TL;DR
A funnel is a line you keep refilling at the top: people go in, customers come out, and you start over. A growth loop is different — the output of each cycle feeds its own next input, so the cost to get one more outcome falls the longer the loop runs.
The funnel you already know
Most teams picture growth as a funnel. You acquire attention at the top, convert some of it to customers in the middle, lose some to churn at the bottom, and then refill the top to do it again. It's a useful picture, and it isn't wrong. It's just a line.
The catch is what happens at the end of each pass. The line resets. Whatever you spent to fill the top last cycle, you spend again this cycle — and usually a little more, because the cheap attention got used up first. A funnel doesn't remember last month. It has to be pushed every single time, and the cost to push it stays flat or climbs. You're not building anything that carries forward. You're keeping a line moving.
What a growth loop is
A growth loop is a system where the output of one cycle becomes the fuel for the next.
That one line is the whole idea. Instead of a path that empties out and has to be refilled from outside, a loop takes what it just produced — a new customer, a published post, a piece of learning — and turns it back into an input for the next round. The thing the loop made last cycle is what powers it this cycle.
Because each pass feeds the next, the loop doesn't start from zero every time. It starts from where it left off. That changes the economics: the work compounds instead of repeating, and the cost to produce one more outcome trends down as the loop runs, rather than staying flat the way a funnel's does.
Funnel vs loop
The point isn't that funnels are bad. It's that a funnel spends to stay still, while a loop spends to build something that makes the next spend cheaper.
A loop you can see
The clearest example is the Content loop Leanboat runs on itself.
It works like this. You publish every day on the channel your buyers already scroll, holding each post to a brand spec. Each post reaches people today — that's the immediate job. But each post does a second job too: it shows you what your audience responds to. You measure which posts earn saves and shares, and that signal decides what you make next. The next post lands harder because it's built on what the last one taught, and because there's now a slightly larger audience to land it on.
That's the loop closing. Reach builds an audience. The audience makes the next post land harder. The measurement makes the next post better. Three things stack at once — the audience, how relevant the posts are, and how recognizable the brand becomes — so the loop gets cheaper and sharper the longer it runs. A cold campaign has to buy attention from scratch. This loop already has it.
Why it matters
This is the difference between compounding and starting over. A funnel asks the same price every cycle to stand in the same place. A loop asks for an investment once and then keeps drawing on it — the audience you built, the relevance you learned, the recognition you earned all carry into the next pass instead of resetting.
It also changes where you start each cycle. A cold campaign begins with strangers and has to pay to turn them into attention. A running loop begins with the attention it already earned. That head start is the whole advantage, and it only exists because the loop fed its own output back in.
Where to go next
A loop only delivers this if it actually closes — if each cycle’s learning changes the next one. Most "loops" don’t. That’s the next piece: Open vs closed loops.
Or browse the full set of loops Leanboat runs at the loops catalog.