Why I Built My Own Finance App (After 9 Years of Google Sheets)
Column XE. That's how far my net worth spreadsheet goes. I've been tracking our finances since the 26th of September 2016 - back when I had my first proper job after University. Nine years of formulas, pivot tables, and a mobile experience that makes me want to chuck my phone in the bin.
Last month, I finally accepted that I'd become the spreadsheet guy who builds an app about it.
The Spreadsheet Problem
Here's the thing - I'm too cheap for Excel. Always have been. So it's been Google Sheets from day one. And honestly? It worked brilliantly for about three years. Then my Wife and I merged our finances properly, and things got difficult.
We'd text each other receipts that never got logged. I'd forget to add the weekly shop. She'd forget about that Amazon order. By month's end, we'd be £200 off budget and having the same conversation: "I thought you logged that?"
The spreadsheet had become a source of friction rather than clarity. But I kept adding columns, formulas, and conditional formatting like that would somehow fix the fundamental problem: it was built for one person, not two.
So I Built Something
I'll be honest - building your own finance app when there are literally hundreds available is peak developer behaviour. It's right up there with building your own static site generator or note-taking app. But here's my excuse: none of them are built for couples who actually want to manage money together without wanting to murder each other.
The first version of personifi was embarrassingly basic. A Next.js frontend, a .NET backend and Postgres. Deployed on my trusty €4.55/month VPS alongside my other experiments.
Three endpoints. Two database tables. One form to add transactions. That was it.
But within a week, my Wife and I were actually using it. No more forgotten expenses. No more duplicate entries. No more "whose coffee was that?" Everything just synced between us instantly.
The Reality of Building It
The couples-first approach threw up interesting problems. How do you handle auth when two people need separate logins but shared data? How do you show who spent what without it feeling like surveillance?
I probably spent too long adding emoji categories. There's something deeply satisfying about seeing 🍺 next to all my pub spending though. Makes the data feel less like accounting and more like... well, life.
The biggest revelation was how little we actually needed. I had grand plans for bank connections, bill predictions, spending insights (and still do). But what do we actually use daily?
- Add transaction (12 seconds on mobile)
- Check this month's total
- See if the other person already logged something
That's it. The boring features were the right features.
What Actually Works
After a month of daily use, here's what's made a difference:
Instant syncing - Not "refresh to see changes" but actual real-time updates. My Wife adds Tesco shopping, it appears on my phone immediately. No more duplicate entries.
Individual logins - We each have our own email login. No shared passwords on sticky notes. When we split up (kidding, love), we can just leave the shared account.
Mobile-first entry - The spreadsheet on mobile was torture. This just works. Standing in Aldi, transaction logged before I've left the till.
The Free Template Escape Hatch
Look, I get it. Not everyone wants to pay for another subscription. And honestly? The spreadsheet worked for years before it didn't. So I've put our original budget template up at personifi.xyz/free-budget-template.
It's a modified UK-focused Google Sheets template we used for nine years. Properly formatted for pounds, categories that make sense for UK spending, and formulas that won't break (probably). Download it, make a copy, use it forever. No email required, no upsell bollocks.
If it works for you, brilliant. When you hit column XE and start questioning your life choices, personifi will still be here.
The Numbers Nobody Asked For
- 47 transactions logged in a months
- 2 daily active users (infinity percent improvement on my usual projects)
- 0 arguments about forgotten expenses (down from weekly)
- £3.93 monthly running cost (Hetzner VPS + Supabase free tier)
- 3 months building the MVP
- too many hours adding features we don't use
- 30 minutes explaining to my Wife why we need another app
What's Next (Whatever You Tell Me)
The roadmap exists but it's written in pencil. Bank connections, fancy reports, spending insights - they're all planned. But I've learned my lesson from building features we don't use.
I want to get this in the hands of actual couples first. See what they complain about. Find out what they actually need versus what I think they need. Maybe you don't care about bank connections because manual entry takes 12 seconds. Maybe you desperately need bill reminders. Maybe you want something I haven't even thought of.
I'm launching it at £4.99/month (both partners included, obviously) with a 30-day free trial. Less than a single coffee that you forgot to track, that Amazon purchase you both logged, or that takeaway that blew your budget because nobody remembered to add it.
If personifi stops even one duplicate purchase or prevents one "we're overspent again" month, it's paid for itself. In our case, it's probably saved us £50 a month just from actually knowing where we stand before making purchases. Not to mention the relationship points from not arguing about money.
At current infrastructure costs I need 4 paying couples to break even. But honestly? I think this provides real value. The spreadsheet was "free" but cost us hours of frustration and genuine arguments. Sometimes paying for the right solution is cheaper than suffering through the wrong one for free.
Will it scale to thousands of users? Probably not without some work. Can it handle a few hundred couples who want to stop arguing about money? Absolutely. When it starts creaking, I'll vertically scale the VPS and worry about proper architecture later.
The feature requests from real couples using it daily will be worth more than any roadmap I could dream up. So yes, those fancy features are coming. But only the ones you actually want.
The Uncomfortable Truth
Building your own solution to a solved problem is usually stupid. There are brilliant apps out there. But sometimes the problem isn't finding a solution - it's finding your solution.
Yesterday, my Wife casually mentioned she actually prefers personifi to the spreadsheet. Not in a "supportive spouse" way (I hope), but genuinely prefers it. After nine years of her tolerating my spreadsheet obsession, dealing with formulas breaking on her phone, and patiently waiting while I "just need to update the budget real quick" - she actually likes using this thing I built. She said logging expenses is actually easy now. That she knows where we stand without asking me to check.
For someone who's built plenty of things that nobody uses (including me after two weeks), hearing that made every hour of debugging, every rejected design, every "why don't we just use YNAB" conversation worth it.
My spreadsheet still exists, frozen at column XE. Nine years of financial history. Haven't opened it in three months.
For a developer who tracks success in GitHub stars and npm downloads, 2 daily active users shouldn't feel like winning.
But it does.
I'd like to acknowledge my companion while creating this article, Claude. While the content of this story is true to my life as I remember it, Claude helped me in crafting it into an engaging text that I hope you enjoy.