This guide explains what each input means, when compound growth is the right model, when simple interest is enough, and how to read a result without treating it like a promise.
The compound mode estimates how a starting balance and recurring monthly savings may grow over time if gains are reinvested. The simple-interest mode estimates a straight-line accrual where gains do not compound.
compound for investing, high-yield savings, or any plan where earnings stay in the account and keep earning.simple when you need a baseline for short-duration or non-reinvested interest.A saver starts with $10,000, adds $500 per month, and assumes a 7% average return for 10 years. The nominal number can look strong, but a more useful planning question is what the final amount still buys after inflation and how much came from contributions versus growth.
Simple interest does not reinvest prior gains. That makes it easier to understand, but usually too conservative for long-term investing and too optimistic for real-world products that include fees or changing terms.
The most useful outputs are usually the trade-offs: how much comes from your own contributions, how much comes from growth, and how sensitive the result is to time and recurring savings. Those trade-offs matter more than the exact ending number.