Compound Interest Calculator

What Is Compound Interest?

Compound interest means growth is calculated on both the money already in the account and growth that has accumulated earlier. That makes the balance capable of accelerating over time instead of increasing by the same fixed amount every period.

If you start with 10,000 and earn 5% for one year, the balance becomes 10,500. If the same 5% applies for another year and the first year's interest remains invested, the next year's growth is calculated on 10,500 rather than only on the original 10,000. That second year therefore adds 525, producing 11,025 before any new deposits.

This calculator goes beyond the basic lump-sum formula. It can model recurring contributions at several frequencies, deposits at the beginning or end of each contribution period, annual increases in the contribution amount, multiple compounding frequencies, extra months and an optional inflation adjustment.

Compound Interest Formula

For a single starting amount with no additional deposits, the standard discrete-compounding relationship is:

For continuous compounding, the growth factor is based on e^{r × t}. The calculator applies the appropriate growth factor to the starting balance and to each recurring contribution according to when that contribution is made.

How Regular Contributions Change Compound Growth

Recurring deposits can matter as much as the interest rate because each deposit becomes additional principal. A deposit made earlier has more time to compound than a deposit made near the end of the projection.

That timing difference is why this calculator does not simply multiply one contribution by the number of periods and pretend all deposits were present from day one. Each scheduled contribution receives only the growth available from its own deposit date to the end of the term.

You can choose weekly, every two weeks, twice monthly, monthly, quarterly or annual contributions independently from the compounding frequency. This is useful when, for example, an account compounds daily but you add money monthly.

Annual contribution increases

If you expect your regular saving amount to rise over time, use the annual contribution increase option. A 3% annual increase means a 250 recurring contribution becomes 257.50 after one completed year, then increases again after the next completed year. This can model a plan where contributions gradually rise with income or with a deliberate savings step-up.

Why Compounding Frequency Matters

Compounding frequency describes how often accumulated interest is added to the balance. With the same nominal annual rate, more frequent compounding generally produces a slightly higher effective annual rate because previously credited interest begins earning growth sooner.

The calculator supports annual, semi-annual, quarterly, monthly and daily compounding, plus continuous compounding. The difference between frequencies can be modest at ordinary rates over short periods, but it becomes more visible as the rate or time horizon increases.

Do not confuse compounding frequency with contribution frequency. One controls how the rate accumulates; the other controls how often new money is added. They are separate settings here because real accounts often use different schedules for the two.

Beginning vs End of Period Contributions

A beginning-of-period contribution is added at the start of each selected contribution interval, giving that deposit one additional contribution period of growth compared with an otherwise identical end-of-period deposit. Over a long horizon, those small timing differences can accumulate.

Use end of period when you want a conservative ordinary-contribution assumption or when deposits occur after each pay/saving period. Use beginning of period when deposits are made immediately at the start of each interval.

Nominal Rate vs Effective Annual Rate

The annual rate you enter is treated as a nominal annual rate for discrete compounding. The effective annual rate shows the one-year growth rate after the selected compounding frequency is taken into account.

This distinction is useful when comparing two assumptions that quote the same nominal rate but compound at different frequencies. It should not be treated as a substitute for an institution's officially disclosed APY or other regulated yield measure, which can depend on product terms and disclosure rules.

What the Inflation-Adjusted Balance Means

A future balance tells you how many currency units you may have under the assumptions entered. It does not tell you what those units may buy in today's terms. If you enter an inflation rate, the calculator discounts the projected final balance back to today's purchasing power.

This is a planning illustration, not an inflation forecast. Actual inflation varies over time, and different goods and services can change in price at very different rates.

Worked Compound Interest Examples

Example 1: lump sum with monthly compounding

Suppose you start with 10,000, use a 6% nominal annual rate, compound monthly and make no additional contributions for 10 years. The calculator applies 0.5% per month across 120 monthly compounding periods. The result is approximately 18,193.97, meaning about 8,193.97 of the ending balance comes from modeled growth.

Example 2: monthly contributions

Now suppose you start with 5,000 and add 200 at the end of every month. At a 5% nominal annual rate compounded monthly for 10 years, each monthly contribution receives a different amount of time to grow. The final balance therefore consists of the original 5,000, 24,000 in scheduled deposits and compound growth earned across the timeline.

Example 3: contribution step-up

If a monthly contribution starts at 300 and rises 4% after each completed year, the deposits in later years are larger than those in the first year. The year-by-year table makes that changing contribution total visible instead of hiding it inside one final number.

How to Use This Calculator Well

1. Enter the amount already available as the starting amount. It can be zero if you are beginning only with future contributions.
2. Enter the annual rate assumption and choose how often that rate compounds.
3. Set the number of years and, if needed, up to 11 extra months.
4. Add a recurring contribution and choose its actual frequency.
5. Select whether deposits occur at the beginning or end of each contribution period.
6. Open Advanced options if you want contributions to increase annually or want to view the final amount in inflation-adjusted terms.
7. Review not only the final balance but also total contributions, growth earned, effective annual rate, chart and year-by-year schedule.

Compound Interest vs Simple Interest

Simple interest calculates interest only from the original principal, so the interest amount is generally linear when principal and rate stay fixed. Compound interest allows previously earned interest to join the balance that can earn future interest. That creates a curved growth path over time.

Recurring deposits add another layer: the account balance changes because of both new money and compounding. For planning, separating money contributed from growth earned is important because a large final balance does not necessarily mean most of that balance came from investment or interest growth.

Important Assumptions and Limitations

The output is a mathematical projection, not a guaranteed account balance or investment return. A constant rate is useful for scenario testing, but real rates and market returns can change. Fees, taxes, contribution limits, withdrawals, minimum balances, product-specific compounding conventions and irregular cash-flow dates can also change actual results.

Daily compounding here uses 365 compounding periods per year. The calculator does not attempt to reproduce every institution's leap-year treatment, day-count convention, transaction cutoff time or promotional rate rule. For a specific financial product, use its official terms when you need product-level precision.

Negative rates are mathematically supported only when the selected compounding structure remains valid. A negative projection rate should not be interpreted as a prediction.

Common Questions

Can I start with zero?

Yes. Enter zero or leave the starting amount blank and provide a recurring contribution. The projection can be built entirely from future deposits.

Does a blank contribution mean zero?

Yes. Optional numeric fields are treated as zero. This lets you calculate a lump-sum investment without recurring deposits.

Can contributions and compounding use different frequencies?

Yes. They are intentionally separate. For example, you can model monthly deposits with daily compounding.

Does more frequent compounding always produce more money?

For the same positive nominal annual rate and otherwise identical assumptions, more frequent compounding generally increases the effective annual rate. The size of the difference depends on the rate and time horizon.

What happens at a 0% rate?

The final balance is simply the starting amount plus all scheduled contributions. No interest or growth is added.

Is the inflation-adjusted balance a forecast?

No. It converts the future balance into today's purchasing-power terms using the inflation rate you choose. It is a scenario, not a prediction of future inflation.

Can I use this for investments as well as savings?

You can use it for hypothetical constant-return scenarios, but investments do not normally earn a guaranteed fixed return. Market volatility, fees, taxes and losses are not modeled.

Why the Year-by-Year Breakdown Matters

A single final number can hide how the result was produced. The schedule separates each year's opening balance, contributions, modeled growth and closing balance. This makes it easier to spot whether your projection depends mainly on your own deposits or on a long period of assumed growth.

The growth chart provides the same idea visually. Early in a long plan, contributions may dominate. Later, if the rate is positive and the balance has become large, annual growth can become a much larger part of the change. That is the compounding effect users often miss when they look only at the final total.

Important: This compound interest calculator provides educational estimates based on the rate, time, contribution schedule, compounding frequency and optional inflation assumption you enter. Actual savings, deposit or investment results can differ because rates and returns may change, fees and taxes may apply, contributions or withdrawals may vary, and financial products can use different compounding or crediting rules. This calculator does not provide individualized financial, investment, tax or legal advice. Last reviewed: September 2026.