Compound Interest Calculator: What Your Monthly Habit Becomes
Most compound interest calculators start with a lump sum you probably don't have sitting around. This one starts where most people actually are: investing a set amount every month. Enter what you're putting in, and see what it actually becomes.
This is a one-time projection based on the numbers you enter, not a live forecast. In the MoneyFlow app, your real net worth, including investment contributions, updates automatically as you log it, so you can see actual progress instead of a hypothetical.
Why the monthly number matters more than the lump sum
Most people don't come into investing with a large lump sum sitting in cash - they build it a paycheck at a time. A calculator built around a one-time deposit answers a question most people aren't actually asking. The more useful question is what a habit you can actually sustain, say $300 a month, turns into after 10 or 20 years of just not stopping. That's usually the more motivating number, because it's tied to something you control every month, not a pile of money you'd need to already have.
A projection, not a promise
The return rate you enter is doing most of the work here, and no one can guarantee what the market actually does over the next 10 or 20 years. Treat the result as a directional estimate, not a guarantee, and try a couple of different rates to see how much your result actually depends on that assumption. What won't change no matter the rate: starting the habit sooner gives compounding more time to work.
Track the real number, not just the projection
This calculator can't know what you actually invest each month, only what you tell it. MoneyFlow tracks your real investment contributions as part of your net worth, alongside spending, debt, and savings goals, so you're watching actual progress build up instead of a one-time hypothetical.
Frequently asked questions
What return rate should I use?+
There's no guaranteed number - it depends what you're invested in. Many long-term planners use 6-7% as a rough, conservative estimate for a diversified stock portfolio after inflation, but actual returns vary a lot year to year. Try a few different rates to see how sensitive your result is.
Does this account for taxes, fees, or inflation?+
No - this is a simple gross-growth projection based on the return rate you enter. It doesn't subtract account fees or taxes, and it doesn't adjust for inflation, so treat the result as a rough estimate, not a guarantee.
How is this different from what MoneyFlow tracks?+
This calculator is a one-time projection based on assumptions you enter. MoneyFlow tracks your actual net worth, including real investment contributions, as it happens, so instead of a hypothetical number you see real progress over time.
Is this calculator free?+
Yes, no sign-up required. Tracking your actual net worth and investment contributions over time is part of the free MoneyFlow app too.
A growth projection is one piece of the picture: track your real net worth or plan a specific savings goal.
Track the real number
Free, offline, and ready in under 2 minutes.