The trip that turned into an app

Somewhere around day nine of an Interrail trip across Europe, one of my co-founders looked up from his phone, holding a fistful of receipts, and said "I have no idea who owes who any more". That sentence is basically the whole reason Deline exists.

How we got there

Three of us set off with a loose plan and a rail pass: hop between cities, figure out the rest as we went, the way you do when you are travelling with people you trust and a plan that is more of a suggestion than a schedule. It was a great trip. It was also, almost immediately, a mess in one very specific way.

Nobody had the full picture. One of us had the hostel booking screenshotted into a WhatsApp thread. Someone else had the train times in their email. A dinner reservation existed only as a memory of "the place with the good pasta near the station, I think". By the third city we were doing the thing every group trip eventually does: standing on a platform asking whether anyone actually knew where we were staying that night.

And then there was the money. Restaurants, groceries, one very necessary emergency umbrella in Vienna, a hostel someone fronted because their card worked and ours did not. Everyone was paying for everyone, in different amounts, in different currencies as we crossed borders, and by the time we were somewhere around Austria nobody could reconstruct who actually owed what.

We tried the usual fixes. A shared notes app. A running tally somebody kept on their phone. It fell apart the same way it always does - not because anyone was careless, but because that is not what a notes app is for.

Building the thing we needed

So we did what I think a lot of people quietly wish they could do when something annoys them enough on a trip: we started sketching out what would actually fix it, right there, using the trip itself as the test case.

The idea we kept coming back to was simple. A trip is not really one thing. It is four things happening in parallel: where you are eating, what you are doing, where you are sleeping, and how you are getting between all of it. Every group chat, every shared doc, every trip-planning method we had ever used treated those as one tangled mess.

What if they were just visually separate, laid out like a map, so you could see the whole shape of the trip at a glance?

That became the core of Deline: a shared timeline built like a metro map, with food, activities, stays and transport each running as their own colour-coded line. Everyone in the group sees the same map, in real time, so the "does anyone know where we are staying tonight" question mostly stops happening. You can see it before you ask it.

The other half, the half that came from that exact moment on day nine, is cost splitting that does the maths nobody wants to do. Add an expense, tag who is in on it, and at the end Deline works out who owes who, collapsing chains of debt so five people are not sending each other seven separate transfers over a pizza.

You can photograph a receipt or a booking confirmation and it reads the details and fills them in itself, which sounds like a small thing until you are the person who would otherwise be typing in a hotel confirmation number at 11pm because everyone is asking where to check in.

What actually changed

We kept building and testing it as we went, city by city, so by the second half of the trip we were not taking screenshots and hoping - we were opening one shared timeline and just knowing.

The receipt scanning in particular is the feature that made me a believer in our own product, mid-trip, in the most unglamorous way possible: not wanting to do arithmetic on a train.

That is really the whole thesis behind Deline. It is not trying to plan your trip for you, or to replace the spontaneity of "let's just wander and see". It is trying to remove the specific, recurring friction of travelling in a group: the scattered bookings, the "who has the confirmation", the end-of-trip maths that always takes longer than it should and somehow always leaves someone slightly annoyed.

Where it stands now

Deline is out on iPhone, built by three people who mostly just wanted to stop arguing about receipts on trains. Android is in progress and there is a waitlist for it.

If you travel in groups - especially the loosely-planned, multi-city, everyone-is-paying-for-everyone kind - I would genuinely like to know what you think. And if you have got your own version of the "who owes who" story, I would like to hear it, because that story is basically how this app got built.

If you are planning one of these trips right now, the two things we wish somebody had told us are in the Interrail guide and in how to split costs on a group trip.