How and Why I Built Simulator Diaries: A Rundown

I’ve wanted to share this for a while, but there’s never a “perfect” time — when you feel fully ready, when every condition is ideal, or your product is polished to the last pixel.

So, here it is. Meet Simulator — a financial planning tool that I’ve been building for over a year now.

How did it start? I’ve always been curious about personal finances — or rather, how to manage mine in a way that gives me control and a sense of stability, more or less.

Everyone around me talks about buying property — because it’s “the smart financial move”. But I absolutely didn’t trust the idea of having a mortgage. It just didn’t fit my lifestyle — and, to be honest, I barely understood how it even works. I figured I’m not the only one.

So, I went looking for tools where I can model some basic scenarios like receiving salary while also paying taxes, contributing towards a pension, mortgage planning, and receiving benefits in kind. Most tools I found — were just calculators. On the other side — great financial advisors (whose services are just as greatly priced).

That’s how the idea of the Simulator was born — not a financial advisor, not a calculator. A tool that helps you simulate life decisions with actual numbers.

Things were getting pretty awkward without a proper structure — until I found Double-Entry accounting beautifully explained by Martin Blais. I really liked the simplicity of it, without me ever needing to understand debit and credit (WTF is that even?). Having some accounts and moving money between them seemed so obvious in hindsight, because that’s precisely what happens in real life too.

Now, the problem was to visualize this… I didn’t like boring lists of transactions, didn’t like seeing final account balances, even the pretty lines and pies didn’t help.

I wanted a MAP. So the Accounts Map was created.

To me, it’s a more detailed and educational way to look at personal finance — letting users track their cash flow and learn something along the way.

Account Mapping focuses on what’s happening in real-world accounts and surfaces some pretty interesting nuances.

For example:

Paying off a mortgage (or any loan) isn’t technically an expense — even though most people count it as one. From a net worth perspective, the real expense is the mortgage interest charged by the bank. The repayment itself is money-neutral. But it carries legal weight — miss a payment, and your house can be repossessed.

I want to capture and visualize small financial nuances like this — so it’s easier to understand how wealth is actually built.

I kept wondering if that’s a good visualization. Then I stumbled upon this post: written by Martin Kleppmann (another Martin?!), which confirmed my idea that a graph with nodes and edges is indeed a decent way to represent the interactions between accounts.

Yet, this simple and easy-to-comprehend view still didn’t solve the problem I was hoping to tackle. So far, I’ve got a tool to calculate and observe, but not something that could plan ahead.

I needed another abstraction… A list of events? It was a decent start for sequential stuff, like a chain of events: get a job, get promoted, maternity leave, quit, but didn’t scale at all with how intertwined financial planning can get. The twisted and mangled DNA of financial life is more like 10 things going on in parallel: main job, side hustle, deposit growing in a bank, stocks plummeting, mortgage interest fluctuating.

… * some days of starting at Windows start up screen and salivating * …

Eureka. There’s a solution! A well-understood visual. A Gantt chart. That’s how project managers plan their work.

But I also realized I’ve seen this idea before. It’s the way a TV guide looks. The matrix of time x channels = content. It’s the way tunes are created in Fruity Loops, Ableton, and DAW. Time x Score = music.

Wouldn’t it be cool to create a financial future the same way your favourite beats are created by the best producers?

So I did it.

It shows important milestones and helps you step away from deep financial details to think in higher-level planning terms, like:

“I’ll get promoted.”
“We’ll go on a vacation.”
“I want to buy X.”

Sure, you could build something similar in Excel. But it becomes kind of hard to understand beyond basic stuff. It’s difficult to achieve visual clarity about timelines and decision-making.

Another high-level view is represented by the dashboard. It gives you a quick overview of the total net worth, cash flow, and bank account balances — you can switch between them with a click.

And if you want to zoom in, you can pick any month and head to the Accounts tab to see what your balance looks like at that point in time.

Now what? Is it fully ready to just simulate whatever future you want?

I’d love to say it all came together smoothly — but the truth is, it took hundreds of iterations, redesigned flows, and more UI tweaks than I can count to make it feel… at least somewhat intuitive.

I really hope to open beta access soon to let everyone try to tune in to their own financial rhythm. If you’re curious to try it out (for free) and give feedback — drop me a line. I’d love to have you onboard!