Move five sliders and watch a lifetime of investing compound in real time. The Engine shows you exactly what you put in, how much the market's compounding added on top, and — the part nobody likes to see — what waiting ten years to start actually costs.
The Engine runs one simple loop, month by month, from your start age to your stop age. Each month your balance earns one month's return and then your contribution is added: balance = balance × (1 + r) + contribution, where r is your annual return divided by 12. The seed amount starts the balance on day one.
Two numbers are tracked the whole way: the running total of what you put in (your seed plus every contribution), and the ending balance. The difference between them is everything compounding added — growth on your money, and then growth on that growth. Early on the two lines sit almost on top of each other. Given enough years, the gap between them becomes the entire story.
That's why the "cost of waiting" bar moves so violently. Delaying the start by ten years doesn't cost you ten years of contributions — it costs you the ten most powerful years, the ones at the far end where the balance is largest and compounding is doing the most work.