Compound interest calculator

You earn a return on your balance, that return is added to the balance, and the next period earns on the larger amount. Over a few years the effect is modest. Over decades it dominates: most of a long-term investment's final value is typically growth rather than the money you contributed.

Usually, yes. Every contribution compounds for the rest of the time horizon, so a steady monthly amount often ends up contributing more to the final balance than a larger one-off deposit made at the start. Time in the market is the lever, and regular contributions buy more of it.

That is your judgment call, not ours. A broad US stock index has historically returned roughly 7% a year after inflation over long periods, but with severe drawdowns along the way. Lower the rate and see how sensitive the result is; if the plan only works at 10%, it is not a plan.

Before. Returns in a taxable brokerage account are reduced by tax on dividends and realized gains. Inside a 401(k) or IRA they compound untaxed, which is precisely why those accounts matter.