The 72-hour interest test: how to validate your startup idea before you spend a penny

You've got an idea. You've been thinking about it in the shower, sketching it on napkins, quietly Googling whether anyone's already built it. And at some point - probably around 2am - you made the leap from "this could be something" to "I need to build this."

Hang on. Not yet.

Because here's what we see all the time at Rise: founders who jump straight from excitement to execution. They spend weeks spec'ing features, months choosing a tech stack, sometimes thousands of pounds on a developer - all before they've answered the only question that actually matters.

Will anyone pay for this?

Not "do people think it's a good idea" (your mates will always say yes). Not "does it solve a problem" (you already believe it does). But will real people, with real money, behave in a way that tells you there's genuine demand? You can find that out in 72 hours. And it won't cost you much more than a long weekend of focused effort.

Why words lie and behaviour doesn't

If you've ever described your idea to someone and they said "oh yeah, I'd definitely use that" - congratulations, you've collected an opinion. Opinions are free, plentiful, and almost entirely useless as validation data. People are polite. They want to be supportive. They'll tell you they love your meal-planning app right up until the moment you ask them to pay £5 a month for it.

Real interest shows up in behaviour, not words. Someone signing up, leaving their email, clicking "notify me when this launches" - that's a signal. Everything else is noise.

So the goal of the 72-hour test isn't to ask people what they think. It's to put something in front of them and watch what they do.

What you're actually going to do

This isn't complicated, and it doesn't need to be polished. You need three things: a simple landing page, a way to reach the right people, and the discipline to read the results honestly. Here's the play.

1. Build a one-page site that describes your product as if it already exists. Not a wireframe. Not a pitch deck. A page that explains what the thing does, who it's for, and what happens next - with a clear call to action. That call to action is the whole point: it might be "join the waitlist", "get early access", or "pre-order now". The specific words matter less than the fact that you're asking people to do something. Tools like Carrd, Framer, or even a basic Webflow page will get you there in a few hours. Don't overthink the design. You're testing demand, not winning a Webby.

2. Drive targeted traffic to the page. And "targeted" is doing a lot of heavy lifting in that sentence. Posting the link on your personal LinkedIn and hoping for the best isn't targeted - it's a prayer. You need to get your page in front of people who actually match your ideal customer. That might mean a small paid ad spend on Meta or Google (£30-50 can get you surprisingly far), posting in niche communities where your audience already hangs out, or sending direct messages to people who fit the profile. Yes, the DMs feel a bit uncomfortable. Do them anyway.

3. Measure what happens - and be honest about it. This is where founders trip up, because the temptation to see what you want to see is enormous. So before you launch the page, write down what "good" looks like. A conversion rate above 5%? Ten email signups from cold traffic? Three people who reply to your DM asking when they can buy it? Set the bar in advance so you can't move the goalposts afterwards.

What counts as a real signal (and what doesn't)

After 72 hours, you'll have some data. But not all data is created equal, and this is where a bit of honesty goes a long way.

A genuine positive signal looks like strangers - people with no social obligation to you - taking an action that costs them something. Even if that "cost" is just an email address, it's a micro-commitment. If people who don't know you are signing up, clicking through, or replying to say "when does this launch?", you've got something worth exploring further.

A false positive looks like your existing network being supportive. Your LinkedIn connections clicking the link because they like you. A mate sharing the post. Lots of page views but no conversions. High traffic from a single Reddit thread where people were arguing about whether the idea was any good. Activity isn't interest. Interest is someone putting their hand up and saying "I want in."

And a negative result? That's not failure - that's the test working. Better to find out now, for free, than six months and £20,000 down the line.

What this test can't tell you

Let's be straight: 72 hours of data from a landing page won't tell you everything. It won't validate your pricing model, your unit economics, or whether you can actually build the thing. It won't tell you if the people who signed up will still care in three months. And it definitely won't replace the deeper discovery work that happens when you sit down with potential customers and really dig into their problems.

But it will tell you whether the core proposition - the thing you're betting on - resonates enough for real people to raise their hand. That's an enormous amount of information for a weekend's work.

You don't need certainty before you start building. You need enough signal to justify the next step.

So what's the next step?

If you run the test and the signals are encouraging, you've got a foundation to build on. If they're flat, you've got an opportunity to rethink - to tweak the proposition, shift the audience, or try a different angle before you've committed any serious resources.

Either way, you're making decisions based on evidence instead of gut feel. And that's the difference between founders who move fast and founders who just move expensive.

At Rise, rapid validation is baked into how we work with founders from day one. We've helped plenty of people run exactly this kind of test - sometimes the result is a green light, sometimes it's a sharp pivot, and occasionally it's an honest conversation about going back to the drawing board. All of those are good outcomes.

If you've got an idea and you want help figuring out whether it has legs, book a free 30-minute discovery call with one of our founders. No pitch, no obligation - just a straight conversation about your idea and what it would take to test it properly. You'll come away with something useful either way.