How to Use
- Enter your starting amount, such as 10,000.
- Set an expected annual return rate, such as 6%, and choose the years to grow.
- Optional: add a recurring contribution, such as 500 per month, and choose monthly or yearly frequency.
- Optional: enter an inflation rate, such as 2%, to compare nominal ending balance with purchasing power.
- Click "Load investing example" to inspect a 10-year monthly contribution scenario in the chart and yearly schedule.
Core Features
- Instant Compound Visualizer: Change return rate, years, or contributions and the stacked chart updates principal vs. gains immediately.
- Monthly or Yearly Contributions: Model monthly contributions, SIP-style investing, yearly additions, or a one-time starting balance.
- Principal vs Interest Breakdown: See total principal, compound gains, ending balance, and ROI percentage without spreadsheet setup.
- Inflation-Adjusted View: Add an expected inflation rate to estimate the purchasing power of the ending balance.
- 100% Client-side Privacy: Your balances, return assumptions, and contribution plan stay in the current browser session.
- Yearly Schedule and CSV Export: Review each year of principal, interest, and balance, then export the projection for planning.
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Calculation Logic
This tool runs a fixed expected-return projection. The calculation advances month by month: each month grows the current balance by the monthly return rate, then adds contributions according to the selected frequency. The yearly schedule summarizes cumulative principal, compound gains, and balance at each year end.
The core relationship is:
ROI is calculated as compound gains divided by total principal:
When an inflation rate is entered, purchasing power is estimated by dividing the ending balance by the inflation factor .
Results are mathematical planning estimates only. They do not include taxes, trading fees, exchange-rate changes, or live market data, and they are not investment advice or a guarantee of returns.
FAQ
Is my financial data private?
Yes. The Investment / ROI Calculator runs locally in your browser and does not send your capital, return rate, inflation assumption, or contribution plan to a server.
How do you calculate ROI with monthly contributions?
The calculator adds your starting amount and each contribution as total principal, subtracts that principal from the ending balance to get compound gains, then divides those gains by total principal.
How does compound interest work?
Compound interest means previous gains can earn future gains. Over longer timelines, reinvested returns become more visible, which is why the interest layer in the chart can grow faster over time.
Should I input my return rate before or after inflation?
Use a nominal annual return if you want nominal dollars. Use a more conservative real return, or enter an inflation rate, if you want to reason about purchasing power.
What is a good expected return rate?
It depends on the asset mix and risk. Diversified stock indexes have historically outpaced cash over long horizons, but past performance does not predict future returns, so conservative assumptions are safer.
Does this predict stocks, funds, or crypto prices?
No. It does not connect to stock, fund, or crypto market APIs. It only projects compound growth from the fixed annual return rate you enter.