Business and Financial Tools
Compound Interest and Investment Growth Calculator
Estimate how a starting balance and end-of-month contributions may grow, including a value in today's money, without sending inputs from your browser.
Private scenario calculator
Compound Interest Calculator
Change any assumption to recalculate instantly. Values stay in this browser and are not saved.
Projected result
Quick answer
How is compound growth calculated with monthly contributions?
The starting balance grows at the net monthly rate, and each end-of-month contribution joins the balance before the next period. The result separates total contributions, estimated growth, and inflation-adjusted value.
How to use this tool
- Enter the starting amount, monthly contribution, and investment period.
- Set assumed return, annual fee, and inflation rates.
- Compare future value, contributions, estimated growth, and value in today's money.
How the calculation works
The calculator subtracts the assumed annual fee from the annual return, converts the effective annual rate with (1+r)^(1/12)-1, and treats contributions as paid at month end. Today's-money value divides the future value by (1+inflation)^years. All rates are constant assumptions, not guaranteed returns.
Examples
| Example | Input | Expected result |
|---|---|---|
| Lump sum only | |
Future value THB 12,100 |
| End-of-month saving with no return | |
THB 12,000, equal to total contributions |
Limitations
- Constant return, fee, and inflation assumptions omit volatility, sequence of returns, and actual losses.
- Taxes, trading costs, changing contributions, and product-specific terms are excluded.
- This is an educational estimate, not advice or a guarantee of return.
Frequently asked questions
What expected return should I enter?
There is no universal value. Test several scenarios based on the relevant asset after fees, without assuming historical returns will repeat.
Are contributions made at the beginning or end of each month?
This calculator treats them as end-of-month contributions, so each starts earning from the following period.
What does value in today's money mean?
It divides future value by accumulated inflation at the entered rate to estimate purchasing power; it is not an inflation forecast.
References
- Stock Exchange of Thailand — Interest and real interest rates Verified 2026-08-03
- U.S. SEC Investor.gov — Compound Interest Calculator Verified 2026-08-03
Content and calculation method last reviewed: