Introduction
I'm a licensed architect who built the bill-splitting and settlement app "FAMI-KAN" entirely on my own. I'm also just an ordinary parent with two kids.
My day job is architectural design. So why would someone from a completely unrelated field end up building a bill-splitting app? In this article, I want to be honest with you, as the developer, about that one question: why. The short answer is that I'd spent nearly twenty years, going all the way back to my college days, dealing with the hassle of splitting bills. That's really the whole story.
It Started With a Notebook and Guesswork in College
I've always loved cars, and I genuinely enjoyed driving. So back in college, whenever friends and I planned a trip, I was usually the one who ended up as the driver. Driving people long distances was never a chore for me.
What was a chore was everything that came after the trip: settling up.
To be clear, we had calculators. It was still the flip-phone era, but basic addition and subtraction weren't the problem. What was missing wasn't a tool to calculate with — it was a system to organize with.
I always kept a notebook where I wrote down "who paid for what": whoever covered the lodging, whoever paid for a group meal, whoever filled up the gas tank. To keep it even a little readable, I remember using different pen colors for different people and lining entries up by date, doing whatever I could to avoid missing anything. I'd gather all these scattered payments into a single notebook and collect everyone's cash in a lump sum on the last day. On top of that, I had to estimate tolls and gas for the drive home in advance, before those costs had even happened.
Looking back, even the way I tallied things up was rough. I'd start by calculating a rough average for the group, then adjust from there by feel — "the younger guys, or anyone a bit tight on cash, should probably pay a little less." In other words, I was doing a kind of manual, weighted bill-split entirely in my head.
The result: the numbers never quite added up. That was just a fact of life. Even with a calculator in hand, the actual organizing and the human judgment calls were still riding on a notebook and gut feeling, so something would always be off by a few hundred yen somewhere. I'd flip back through the notebook and start over. I repeated that ritual on every single trip. I was young enough to just laugh it off at the time, but looking back, that was the beginning of my very long relationship with splitting bills.
Adulthood Brought the Same Wall
Time passed. The college kids became working adults, then parents. Flip phones turned into smartphones, and calculators turned into apps. And yet — the hassle of splitting bills hadn't gone away at all.
One moment really captures it: our family's annual New Year party. That year, it was six households — eight adults and eight kids, sixteen people in total. We rented a venue, had a meal, and moved on to a second gathering while the night was still young. Fun time flies. And then, in the final thirty minutes of the night, while everyone else was having a great time at the after-party, I was the only one staring down my phone's calculator app.
Settling up that night was never going to be as simple as "total divided by headcount." The same set of thoughts was always swirling in my head:
- "We probably want a different amount for adults versus kids."
- "Whoever didn't drink much should probably pay a bit less."
- "Everyone should split the venue fee, but only the people who came to the after-party should split that bill."
The tools had come a long way since my college days, but the core hassle — organizing everyone's scattered payments while also accounting for each person's individual circumstances — hadn't been solved at all in nearly twenty years. Calculators got faster, but the actual work still depended entirely on my own head and scribbled notes. I'd redo the math half a dozen times late into the night, and eventually just round things off by quietly covering the difference myself because it was easier than arguing over a few hundred yen. On the drive home that night, I finally thought it, seriously this time: "If an app could just calculate all of this in one shot, that would be amazing."
The Hassle Wasn't Just for the Organizer
There's one more scene I haven't forgotten. This time I wasn't the organizer — I was on the other side, as a participant.
At one gathering, the group decided to use a bill-splitting tool to settle up. But I didn't feel like downloading an app just for that one occasion, so I never installed it. Which meant I had to tell the organizer how much I'd spent, out loud, whenever there happened to be a free moment. Having to stop and think "wait, how much was that again?" in the middle of some random conversation was a quietly annoying kind of friction.
And then, finally, the settlement results came through. All I got was a number. If I wanted to understand why I owed exactly that amount, there was no way to find out. Both the organizer and the participants were carrying their own small piece of stress. That's when it really clicked for me: the hassle of splitting bills isn't only a problem for "the person doing the calculating."
That's why FAMI-KAN never requires participants to download an app or create an account. The organizer just sends a URL, and whoever receives it can open it directly. And rather than simply handing people a final number, it's built so each person can see exactly why their amount comes out the way it does — because I wanted to take away even a little of that vague, uneasy feeling I remembered from the participant's side of the table.
So I Built It Myself
Once I'd made up my mind, I didn't stop. I spent every weekend on development, doing nothing else but sleep, and stayed up late into the night on weekdays after finishing my regular job. I kept that pace up for about two weeks, and the first version of FAMI-KAN took shape. There was only ever one motivation behind it: never let "the numbers don't add up" happen again — and give organizers back the thirty minutes that settling up used to steal from them.
What I Cared About Most: Turning Complex Math Into a Simple Screen
The hardest part of development wasn't the technical side — it was figuring out how to turn a genuinely complicated bill-split into a screen anyone could use without hesitation. The calculation itself is something a computer can solve instantly, once you feed it the right conditions. The real problem is that if the screen for entering those conditions is complicated, you're right back to the same mess as that old notebook or a spreadsheet.
I kept coming back to one goal: "my wife, or any of the moms in her friend group, should be able to use this without getting confused." I stripped down and rearranged the input flow over and over with that single standard in mind. No account creation, no app install required — just open a browser, enter names and amounts, and you're done. A large share of my development time went into making sure the entry barrier was as close to zero as possible.
People often ask, "why would an architect build an app?" but honestly, it's not as much of a leap as it sounds. The way of thinking I picked up through architecture — design the whole first, break it down into parts, then assemble them one by one — carried over directly into building an app. It felt strikingly similar to drawing up a blueprint.
What FAMI-KAN Can Do
I designed it to directly solve the exact situations I'd personally run into, from my college days all the way to that New Year party.
- Different amounts for adults and kids: Kids can pay a reduced amount, or nothing at all. Just set a ratio and the app calculates the rest automatically.
- Weighted amounts for drinkers versus non-drinkers: You can reflect "people who drank a lot pay more, people who didn't pay less" as a ratio. It turns the same manual "average, then adjust by feel" judgment call I used to make in college into an actual built-in mechanism.
- Grouping by household: Couples or families who share a single wallet can be treated as one settlement unit, so you never end up with a confusing situation where a husband and wife get billed separately.
- Settling multiple people's advance payments with the fewest possible transfers: This is exactly the work I used to do by lining up color-coded, scattered payments in a notebook. No matter who paid for what, the app automatically works out who needs to pay whom, and how much, using the smallest possible number of transfers so everyone ends up even.
- Sharing results with a single URL: Just send the link to the calculation, and everyone can check their own amount (for the actual payment, use whatever method your group prefers — bank transfer, a payment app, or otherwise).
Getting Back Those "Last Thirty Minutes"
It's been a long time since the days of flipping through a color-coded notebook to fix a few-hundred-yen discrepancy. What I want FAMI-KAN to achieve really comes down to one thing: giving organizers back the time that settling up used to take from them.
I want that time to go toward the people and kids right in front of you, not toward a calculator. It's a small, unglamorous kind of stress, but it comes up every single time — and as someone who's lived with it for twenty years, I keep building this app hoping I can make it a little lighter for everyone else too.
If you ever find yourself stuck as the organizer again, I hope you'll give it a try. No account, no download required. I hope it gives you back a little more of your own time.