Compound Interest Calculator: Project Future Value With Monthly Contributions
This compound interest calculator shows how your rental income grows when you reinvest returns over time.
The lump sum you're starting with today — your principal, the base amount on which all future compounding begins.
The fixed amount you add each month after the initial deposit. Consistent contributions often matter more than the starting balance over a 10-plus-year period.
Your expected yearly growth rate as a percentage. Use a conservative figure — 5–7% is a common benchmark for diversified portfolios.
How long you plan to leave the money growing. Time is the single biggest driver of compounding results.
Your projected total balance at the end of the investment period, including principal, contributions, and compounded interest.
How a Compound Interest Calculator Helps You
TrendingUp | See Growth at a Glance
Instantly shows how your rental revenue compounds over years, so you can set realistic portfolio targets.
RefreshCw | Run Scenarios Fast
Swap contribution amounts or return rates in seconds to compare reinvestment strategies without rebuilding spreadsheets.
DollarSign | Quantify Every Decision
Puts a real number on what delaying investment by 12 months actually costs your long-term returns.
How the Compound Interest Calculator Works
Enter four numbers. The calculator handles the rest, projecting your investment's growth over time using standard compound interest math applied monthly.
Initial Investment
The lump sum you're putting in on day one — your starting principal.
The larger your starting principal, the greater your compounding base from the outset.
Monthly Contribution
The fixed amount you add each month after the initial deposit.
Consistent contributions often matter more than the starting balance over a 10-plus-year period.
Annual Return Rate (%)
Your expected yearly growth rate as a percentage. Use a conservative figure — 5–7% is a common benchmark for diversified portfolios.
Investment Period (Years)
The lump sum you're putting in on day one — your starting principal.
The larger your starting principal, the greater your compounding base from the outset.
Run Your First Calculation Today
See exactly how compound interest builds your STR reinvestment over time.
No credit card required. Cancel anytime.
Frequently Asked Questions
What's the Difference Between Monthly and Annual Compounding in This Calculator?+
This calculator compounds monthly by default, meaning interest is calculated 12 times per year. Monthly compounding produces a higher future value than annual compounding on the same principal, a gap that widens the longer your investment period runs.
Does the Monthly Contribution Field Assume Contributions at the Start or End of Each Month?+
Contributions are applied at the start of each period so each deposit earns a full month of interest before the next cycle. This produces slightly higher projections than end-of-period contributions.
Can This Tool Model a Declining Return Rate Over Time?+
No, the Annual Return Rate (%) field accepts a single fixed rate for the full investment period. If you expect rate changes, run separate calculations for each phase and combine the results.
How Accurate is the Future Value Output for Real-world Investment Planning?+
The output assumes a constant return rate with no fees, taxes, or inflation adjustments. Treat it as a directional benchmark, not a precise financial forecast.
What Should STR Hosts Enter as an Annual Return Rate for Reinvested Rental Income?+
A conservative range is 6–8% annually, reflecting typical diversified index fund returns. Hosts reinvesting STR profits into higher-yield instruments might model 10–12%, though that carries meaningfully higher risk.