I like making the numbers make sense.

I'm Luna Lee, a backend software engineer (formerly at Amazon Health and One Medical) with UCLA degrees in financial actuarial mathematics and statistics. I build small, honest tools and write about money with the math shown.

61 monthsTo repay $1,200 at 24.99% APR paying $35/month, with $925.71 in interest.Try the calculator → $2,670Estimated move-in cost for a $1,050/month California rent share, including deposit, fees, setup, and moving.See Chapter 4 breakdown → $2,724Estimated monthly take-home on $19/hour in California, after taxes and paycheck deductions.See Chapter 1 breakdown →

Selected work

Writing and tools built around practical problems: understanding money, checking the math, and finding words for a difficult situation.

Writing — free posts + full book

First 90 Days

Written and built for teens moving out: worked examples for a first paycheck, apartment, and credit card, plus a free calculator. The full 12-chapter book is available on Gumroad for $15.

Read the free chapters →

Tools

FM Toolkit Calculators

Interactive interest theory and loan amortization tools for Exam FM, checked against known-answer examples. Try the free calculators or get the full bundle.

See the calculators →

Code

fm-formalization

Interest-theory results formalized in Lean 4 with Mathlib, including accumulation and discount factors and the geometric series behind annuity formulas.

View on GitHub →

Interactive tool

Boundary Check

An interactive boundary-setting tool for putting a difficult situation into words and finding a clear next step.

Try Boundary Check →

Interactive tool

Uncertainty Sandbox

A simple scenario planner for examining a worry through your estimates of impact and likelihood, alongside the resources and fallback options you can draw on.

Explore a scenario →