A compound interest calculator can answer “what if” questions, such as what a lump sum today might be worth in several years or how regular savings might grow by a target date. It calculates from the figures entered; it does not predict actual returns or guarantee a future balance.
The future value formula for a lump sum
For a single principal compounded once per period, use FV = PV × (1 + r)n. PV is the principal today, r is the return rate per period, and n is the number of compounding periods. The Stock Exchange of Thailand explains time value of money and compound interest in its time value of money lesson.
A repeatable calculation example
Assume a principal of THB 100,000, no additional deposits, a 5% annual rate, annual compounding, and a 10-year period: 100,000 × (1 + 0.05)10 = THB 162,889.46, or about THB 162,889 before fees, taxes, and inflation. This is a mathematical result from the assumptions, not a forecast that an investment will earn 5% every year.
Change the rate or time period in our compound interest calculator and compare scenarios. Changing one assumption can substantially alter the final figure.
A lump sum and regular savings need different inputs
The lump-sum formula above does not include later deposits. If you plan to save monthly, use a tool that accepts the deposit amount, frequency, and timing; check whether deposits are made at the beginning or end of each period. The Bank of Thailand says savings calculator results are estimates and recommends asking a financial institution for details when they relate to an actual product (the Bank of Thailand savings calculator).
Check assumptions before using the result
- Is the rate entered per year or per month, and does it match the compounding frequency?
- Will you make additional deposits or withdrawals, and does the calculator support that pattern?
- Does the result show a balance before or after fees and taxes?
- After accounting for inflation, would that amount still meet your goal?
- Is the return rate only an assumption, or does it relate to a product with specific risks and terms?
To see how inflation affects a goal, read how to think about returns after inflation. If you are allocating income, start with the 50-30-20 budgeting framework and adjust it to your actual expenses.
Article scope and referenced video
This article explains the formula and how to read a simulated result, using SET and Bank of Thailand sources. The YouTube video retained on this page discusses dividend funds, not calculator formulas, so it is not used to verify the article.
Frequently asked questions
Can a compound interest calculator predict returns?
No. It calculates based on the assumptions entered by the user. The result is not a guarantee or a return estimate for any investment product.
Why do two calculators produce different results?
Check whether the rate is annual or per period, the compounding frequency, whether deposits occur at the beginning or end of each period, and whether fees, taxes, or inflation are included. Calculators may use different assumptions.