Compound Interest Calculator (Investment)
Estimate future investment value from an initial amount, monthly contributions, annual return, term, tax settings, and inflation-adjusted present value including the purchasing-power loss from inflation.
Compare lump sums, monthly investing, taxes, and inflation together
Enter your investment assumptions to see estimated total assets, returns, after-tax value, real purchasing power, and year-by-year growth on one screen.
Calculate future value or work backward from a target amount to the required inputs.
Enter investment assumptions to see total assets, returns, taxes, and real purchasing power in order.
Present value = nominal total assets ÷ (1 + inflation rate)^investment term
| Year | Cumulative principal | Investment return | Total assets | Return rate |
|---|---|---|---|---|
| Year-by-year accumulated amounts appear after calculation. | ||||
What is a compound interest calculator?
A compound interest calculator estimates future assets when compounding is applied to an initial investment and recurring monthly contributions. It supports lump-sum investing, monthly investing, and a combined approach, with compounding frequencies from annual to daily.
For investment planning, you can compare reference taxable, preferential, and tax-free scenarios and also convert the future amount into inflation-adjusted present value to understand real purchasing power.
Who this is useful for
- People planning long-term investing – Anyone investing part of their income regularly and checking estimated assets 20 or 30 years ahead
- Investors putting a lump sum to work – Anyone estimating the compounding effect of deposits, funds, ETFs, or similar products
- People preparing for retirement funding – Anyone working backward from a retirement target to a required monthly contribution
- People comparing tax scenarios – Anyone comparing after-tax outcomes between standard taxable and preferential or tax-free scenarios
- Parents planning education or future family costs – Anyone estimating how much to invest now for a lump sum needed 10 to 20 years later
Key features
- Future value – Automatically estimate future assets from initial investment, monthly contribution, annual return, and term
- Goal back-solve – Work backward from a target to the required contribution, starting amount, return, or term
- Multiple compounding frequencies – Choose annual, semiannual, quarterly, monthly, or daily compounding
- Contribution timing – Distinguish beginning-of-month and end-of-month contributions for more accurate projections
- After-tax return calculation – Compare reference taxable, preferential, and tax-free after-tax outcomes
- Inflation adjustment – Check real purchasing power as an inflation-adjusted present value
- Rule of 72 – Show an estimated time for principal to double
- Doughnut chart – Visualize the ratio of principal to return
- Year-by-year growth chart – See how assets grow each year in a bar chart
- Year-by-year schedule – Review cumulative principal, return, total assets, and return rate by year
- Excel download – Save the year-by-year investment schedule as an Excel file
How to use it
- Choose a calculation type – Select the “Future value” or “Goal back-solve” tab.
- Enter investment assumptions – Enter the initial investment, monthly contribution, annual return, and investment term. You can use only an initial amount, only contributions, or both.
- Choose compounding frequency – Choose a compounding frequency from annual to daily. Monthly compounding is the default.
- Set after-tax return – Enable “Apply after-tax return” to select a tax setting.
- Set inflation – Enable “Apply inflation rate” to convert the headline result to present value while also showing the nominal amount separately.
- Run the calculation – Review estimated total assets, return mix, and the year-by-year schedule.
- Use the goal back-solve – Enter the target amount and assumptions to calculate the required input.
Compound interest formula
Compound interest means returns are earned not only on the principal but also on prior returns. Unlike simple interest, the effect accelerates as the time horizon gets longer.
Lump-sum investment
A = P × (1 + r/n)nt
A: final amount, P: initial investment, r: annual return, n: compounding periods per year, t: investment term in years
Monthly contribution
FV = PMT × [(1 + r/n)nt − 1] / (r/n) (end-of-month contribution)
FV = PMT × [(1 + r/n)nt − 1] / (r/n) × (1 + r/n) (beginning-of-month contribution)
FV: future value of contributions, PMT: monthly contribution, r: annual return, n: compounding frequency, t: investment term
Combined lump sum + contributions
The result adds the compounded value of the initial investment and the compounded future value of monthly contributions.
Rule of 72
Time to double principal (years) ≈ 72 ÷ annual return (%)
Example: at a 7% annual return, 72 ÷ 7 ≈ about 10.3 years for principal to double.
Investment tax settings (2026 reference)
| Tax setting | Rate | Tax-free threshold |
|---|---|---|
| Standard taxable setting | 15.4% reference rate | None |
| Preferential tier A | 9.9% on the portion above the threshold | 5,000,000 |
| Preferential tier B | 9.9% on the portion above the threshold | 10,000,000 |
| Tax-free setting | 0% | All profit tax-free |
Tax note: These tax settings are simplified comparison scenarios. Actual tax rates, allowances, reporting rules, and eligible accounts vary by jurisdiction, product, and personal situation, so confirm with official sources or a qualified professional before making decisions.
Frequently asked questions
What is the difference between compound and simple interest?
Simple interest earns returns only on the principal, while compound interest earns returns on both the principal and previous returns. The longer the horizon, the more visible the compounding effect becomes.
Is monthly or annual compounding better?
A shorter compounding interval is generally more favorable because returns are added back sooner. Monthly compounding usually grows slightly faster than quarterly or annual compounding, but real products use the frequency defined in their terms.
How much can tax-advantaged settings change the result?
The preferential tiers on this page are reference scenarios for comparing after-tax results. Real account names, limits, eligible products, and tax rates depend on your location and account type.
Why should I include inflation?
Inflation reduces purchasing power. When inflation is enabled, the large future amount is divided by (1 + inflation rate)^investment term to convert it into present value. This helps separate nominal gains from real gains.
What is the Rule of 72?
The Rule of 72 is a quick way to estimate how long it takes for principal to double. Divide 72 by the annual return percentage to get an approximate number of years.
What is the difference between beginning-of-month and end-of-month contributions?
Beginning-of-month contributions are invested from the start of each month, while end-of-month contributions begin compounding one month later. The gap may be small at first, but it grows with larger amounts and longer terms.
No comments yet. Leave the first opinion.