Investment Growth Calculator
See what a starting amount plus regular monthly contributions could grow into — and just as importantly, what that future number is actually worth once inflation quietly eats into it.
Think of it like a garden, not a lottery ticket
Investing isn’t about picking one lucky moment — it’s closer to planting a garden. Your starting amount is the seed. Your monthly contribution is showing up regularly to water it. The return rate is how good the growing conditions are. None of those things alone make a garden thrive — it’s the combination, kept up consistently, that eventually produces something much bigger than what you originally planted.
Why “today’s dollars” matters more than the big final number
Imagine your grandmother tells you she bought a house for $20,000. That sounded like a fortune then, but it wouldn’t buy much of a house today — prices simply rose over time. Your investment’s future value has the same issue: a future balance of $150,000 sounds great, but if prices have roughly doubled by the time you get there, it only buys what about $75,000 buys today. That’s why this calculator shows both numbers side by side — the raw future total, and what that total is actually worth once you translate it back into today’s buying power.
Does it matter if you contribute at the start or end of the month?
Slightly, yes. If your contribution lands at the beginning of the month, it has a few extra weeks to grow before the month’s return is calculated, compared to landing at the end of the month. Over a year the difference is small; over 20-30 years, it can add up to a genuinely noticeable amount — which is why this calculator lets you toggle between the two.
- Consistency beats timing. Showing up every month, even with a smaller amount, tends to outperform waiting for the “perfect” moment to invest a lump sum.
- Small monthly amounts compound too. As the coffee example shows, the size of a single contribution matters far less than doing it every single month without fail.
- Always sanity-check against inflation. A return rate that barely beats inflation means your money is treading water, not actually growing in real terms.
Frequently asked questions
No. This tool assumes a steady, consistent annual return for simplicity — real investments go up and down year to year. Treat the result as an estimate based on an average, not a promise.
No — taxes on gains and any account/management fees will reduce your real-world result below what’s shown here. Tax-advantaged accounts can help minimize that gap.
A common, conservative starting point is 6–8% for a diversified stock portfolio over the long term, and lower (2–4%) for more conservative holdings like bonds or savings accounts. Adjust based on where you’re actually planning to invest.
That’s completely normal — use your realistic average monthly contribution rather than your best-case number. It’s fine to re-run this calculator periodically as your situation changes.
Want a fair yearly rate to compare this against other investments?
Try the CAGR Calculator next.
CAGR Calculator Compound Interest Calculator Back to Toolkit