Note : This calculator estimates compound-interest growth from fixed assumptions. It does not include fees, taxes, inflation, variable interest rates, missed deposits, withdrawal penalties, changing deposit amounts, or investment risk.

Use this Compound Interest Calculator to estimate final balance, total contributions, interest earned, and effective annual rate from an initial balance, annual interest rate, term, compounding frequency, and optional recurring deposits. It is useful for savings accounts, investment projections, deposit plans, and long-term growth estimates.

Reviewed by: AjaxCalculators Editorial Team
Last updated: April 26, 2026
Method source: Standard compound-interest formulas using principal, annual interest rate, compounding frequency, time, and optional fixed recurring deposits
Editorial standards: AjaxCalculators Editorial Policy

What This Compound Interest Calculator Calculates

This calculator estimates:

• Final balance
• Total contributions
• Interest earned
• Effective annual rate
• Growth summary
• Step-by-step calculation

The live tool uses your initial balance, annual interest rate, years, extra months, compounding frequency, and optional recurring deposits. It also lets you choose whether deposits are made at the beginning or end of each deposit period.

What Compound Interest Means

Compound interest means interest is calculated not only on the original principal but also on interest that has already been added to the balance.

In simple terms, compound interest is interest on interest. Over time, this can make a balance grow faster than simple interest, especially when the term is long, the interest rate is higher, or compounding happens more often.

How the Compound Interest Calculator Works

1) Compound Interest Formula Without Recurring Deposits

For a starting balance with no additional deposits, the standard compound-interest formula is:

Final balance = P × (1 + r ÷ n)^{n × t}

In this formula:

• P is the initial balance or principal
• r is the annual interest rate as a decimal
• n is the number of compounding periods per year
• t is the time in years

2) Interest Earned

Interest earned is the amount gained above the money you contributed.

Interest earned = final balance − total contributions

If there are no recurring deposits, total contributions are usually the same as the initial balance. If recurring deposits are used, total contributions include the starting balance plus all deposits added during the term.

3) Total Contributions

Total contributions represent the money you personally added.

Total contributions = initial balance + total recurring deposits

This helps separate your own deposits from the interest generated by compounding.

4) Effective Annual Rate

The effective annual rate shows the annual return after compounding frequency is included.

Effective annual rate = (1 + r ÷ n)ⁿ − 1

To display it as a percentage:

Effective annual rate % = [(1 + r ÷ n)ⁿ − 1] × 100

For the same annual interest rate, more frequent compounding usually produces a slightly higher effective annual rate.

5) Recurring Deposits

The calculator also supports optional fixed recurring deposits. These deposits can be added yearly, monthly, bi-weekly, or weekly, depending on the option selected.

Recurring deposits increase the final balance because more money is added over time and those deposits may also earn compound interest.

If deposits are made at the end of each period, they start earning interest after they are added. If deposits are made at the beginning of each period, each deposit has more time to grow, so the final balance is usually higher.

Compounding Frequency Options

The compounding frequency controls how often interest is added to the balance.

Compounding Option	Periods Per Year
Yearly	1
Semi-annually	2
Quarterly	4
Monthly	12
Bi-weekly	26
Weekly	52
Daily	365

For the same starting balance, rate, and term, daily compounding usually produces a slightly higher balance than yearly compounding. The difference is often small over short periods but can become more noticeable over long periods.

Compound Interest With Recurring Deposits

Recurring deposits can have a major effect on long-term savings growth. The final balance comes from two parts:

• growth of the initial balance
• growth of each recurring deposit after it is added

For example, saving $100 every month for several years can produce much more growth than starting with one balance and never adding more money. This is because each deposit increases the base that can earn interest.

Deposit Timing: Beginning vs End of Period

The calculator includes a deposit timing option:

• End of each period: deposits are added after that period’s growth cycle.
• Beginning of each period: deposits are added earlier and may earn interest for more time.

When all other inputs are the same, beginning-of-period deposits usually produce a higher final balance than end-of-period deposits.

Assumptions and Important Notes

• This calculator assumes a fixed annual interest rate.
• It assumes interest compounds at the selected frequency.
• It assumes recurring deposits are fixed and made consistently.
• It does not include fees, taxes, inflation, account minimums, early withdrawal penalties, or variable-rate changes.
• It does not model market volatility, investment losses, or changing contribution amounts.
• It does not guarantee future returns.
• For real savings or investment decisions, compare the calculator estimate with actual account terms and product disclosures.

Worked Example: Compound Interest Without Deposits

Suppose you start with $5,000, earn a 6% annual interest rate, and compound monthly for 3 years.

Step 1: Convert annual rate to decimal
6% = 0.06

Step 2: Identify compounding periods
Monthly compounding means n = 12

Step 3: Convert time to years
3 years = 3

Step 4: Apply the compound-interest formula
Final balance = 5,000 × (1 + 0.06 ÷ 12)^{12 × 3}

Step 5: Calculate
Final balance ≈ $5,983.40

Step 6: Find interest earned
Interest earned = 5,983.40 − 5,000 = $983.40

So, $5,000 at 6% compounded monthly for 3 years would grow to about $5,983.40 before fees, taxes, or withdrawals.

Worked Example: Compound Interest With Monthly Deposits

Suppose you start with $1,000, add $100 each month, earn a 5% annual interest rate, and save for 2 years.

Step 1: Identify the starting balance
Initial balance = $1,000

Step 2: Find total recurring deposits
$100 × 24 months = $2,400

Step 3: Find total contributions
Total contributions = 1,000 + 2,400 = $3,400

Step 4: Apply compound growth to the starting balance and deposits
Each deposit is added over time and can earn interest after it enters the account. Deposits made earlier have more time to grow than deposits made later.

Step 5: Interpret the result
The final balance will be higher than $3,400 if interest is earned, because the account includes both contributions and compound interest.

How to Use This Compound Interest Calculator

1. Select the currency symbol you want to display.
2. Choose the compounding frequency.
3. Enter the initial balance.
4. Enter the annual interest rate.
5. Enter the number of years and any extra months.
6. Select a recurring deposit frequency, or choose never if you do not want to add deposits.
7. Enter the deposit amount if recurring deposits are used.
8. Select whether deposits happen at the beginning or end of each period.
9. Click Calculate.
10. Review final balance, total contributions, interest earned, effective annual rate, summary, and step-by-step output.

How to Interpret the Result

Final balance is the estimated ending account value after interest and recurring deposits are included.

Total contributions show how much money you personally added, including the initial balance and recurring deposits.

Interest earned is the estimated growth above your contributions.

Effective annual rate shows the annualized effect of the interest rate after compounding frequency is included.

Summary gives a quick plain-language overview of the growth result.

Step-by-step output shows how the calculator reached the estimate.

Compound Interest vs Simple Interest

Simple interest is calculated only on the original principal.

Compound interest is calculated on the principal plus previously earned interest.

That difference is important over long periods. With compound interest, interest can begin earning more interest, which can accelerate growth over time.

Why Time Matters in Compound Interest

Time is one of the most important inputs in compound-interest growth. The longer money stays invested or saved, the more opportunities it has to compound.

For example, a 5-year savings period and a 20-year savings period can produce very different results, even with the same starting balance and interest rate. Recurring deposits also become more powerful when they are made consistently over many years.

Practical Uses of a Compound Interest Calculator

• estimate savings account growth
• project investment growth under a fixed return assumption
• compare compounding frequencies
• see the effect of monthly or weekly deposits
• estimate interest earned over time
• compare beginning-of-period and end-of-period deposits
• plan long-term saving goals
• understand how compounding affects money growth

Common Mistakes to Avoid

• Do not confuse annual interest rate with effective annual rate.
• Do not ignore fees or taxes when estimating real returns.
• Do not assume a fixed rate will stay unchanged if the actual account has a variable rate.
• Do not treat projected investment growth as guaranteed.
• Do not forget that withdrawals reduce the balance that can compound.
• Do not compare accounts using rate alone if compounding frequency and fees differ.
• Do not use this calculator as a full retirement, tax, or investment-planning model.

Formula Summary

What You Want to Find	Formula
Final balance without deposits	Final balance = P × (1 + r ÷ n)n × t
Effective annual rate	EAR = (1 + r ÷ n)n − 1
Total contributions	Total contributions = initial balance + total recurring deposits
Interest earned	Interest earned = final balance − total contributions
Recurring deposit total	Recurring deposit total = deposit amount × number of deposits

References

1. AjaxCalculators live Compound Interest Calculator
2. FDIC: Compound Interest
3. Consumer Financial Protection Bureau: Annual Percentage Yield calculation rules
4. Investor.gov: Compound Interest Calculator
5. Investopedia: Compound Interest explanation and formula

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Financial note: This calculator is for educational and planning use only. It estimates compound-interest growth from the values entered and does not provide financial, investment, tax, accounting, legal, or banking advice. Actual results can differ because of fees, taxes, inflation, variable rates, missed deposits, withdrawals, penalties, account rules, investment risk, and changing market conditions. For real savings or investment decisions, review official account terms and consider speaking with a qualified financial professional.