I built a free iOS app to answer one question: How do children fit into your financial future?

A few months ago I started wondering how having children would actually affect my long-term financial picture — not in a vague "kids are expensive" way, but concretely. How much would childcare cost in my area? What would college do to my savings rate? How many years would it push back financial independence?

I couldn't find a tool that answered those questions in one place, so I built one.

What FinSim does

FinSim is a free iOS financial simulator that runs two scenarios side by side — your wealth trajectory with children and without — so the trade-off is immediately visible rather than something you have to calculate yourself.

It models:

• Child costs using real NDCP childcare data by county (3,200+ US counties)

• Per-child birth age control so costs kick in at the right point

• Debt payoff timeline and its effect on long-term wealth

• Retirement drawdown based on the 4% rule

• Financial independence age and how each decision shifts it

The technical side

Built entirely in SwiftUI as a solo project. The financial projection engine runs four simulation passes per calculation — two for FI age detection without retirement applied, two for the actual chart with retirement drawdown. Child costs are modeled with age-specific cost curves (childcare ages 0-4, living costs 0-17, education 5-17, college 18-21) inflated at 5% annually since childcare costs historically outpace general CPI. Tax rates use a simplified bracket approximation rather than a flat rate.

Everything runs on-device. No account, no data collection, no subscription.

What I learned building it

The hardest part wasn't the math — it was making the financial model honest without making it intimidating. Early versions of the app were technically more accurate but surfaced numbers that scared people without giving them enough context to act on them. I spent a lot of time on the framing and the disclaimer layer to make sure the output was useful rather than just alarming.

The other thing I underestimated was regional variation in childcare costs. The NDCP dataset covers 3,200+ counties and the spread is enormous — infant care in some California counties runs nearly 3x what it costs in rural Midwest counties. A flat national average would have made the model meaningfully wrong for a large share of users.

Where it stands

Just launched on the App Store. Free, no ads, no in-app purchases. Early reviews are positive. Now focused on getting it in front of the right people and figuring out what to build next based on real user feedback.

Happy to talk through any of the modeling decisions or the SwiftUI architecture — and genuinely curious whether anyone here has thoughts on the right next feature (home purchase modeling, partner income, Monte Carlo, Social Security estimates are all on the list). Thanks everybody!

FinSim launches on Product Hunt this upcoming Tuesday, July 14!