Compound Interest Calculator

Project nominal and inflation-adjusted investment growth with customizable compounding frequency and deposit timing.

Projected Future Balance (Nominal)
USD 343,778.24
USD 209,797.87 in today's purchasing power (2.5% inflation)
Total Contributions USD 130,000.00
Total Compound Interest USD 213,778.24
Inflation-Adjusted Value USD 209,797.87
Effective Annual Yield 8.3%
Inputs
⚡ Scenarios:
Amounts are treated in the selected currency; no foreign-exchange conversion is applied.
USD ($)
Starting lump-sum deposit at Day 0.
USD / mo
Recurring amount added every month.
% / yr
Expected annual rate before inflation.
years
Number of years funds remain invested.
How often interest is credited to the principal balance.
Whether monthly deposits earn interest during their first month.
% / yr
Used to discount future nominal balance into today’s dollars.
Results & Graph
Projected Future Balance (Nominal)
USD 343,778.24
USD 209,797.87 in today's purchasing power (2.5% inflation)
Total Contributions
USD 130,000.00
USD 10,000.00 initial + USD 500.00/mo
Total Compound Interest
USD 213,778.24
62.2% of ending balance
Inflation-Adjusted Value
USD 209,797.87
At 2.5% annual inflation
Effective Annual Yield
8.3%
Compounded 12x/year

Contributions vs. Compound Growth Over Time

Principal deposits stacked with cumulative compound earnings by year
Graph 1 • Initial Principal vs. Monthly Deposits vs. Compound Interest Compound interest generates 62.2% of your ending wealth (Rule of 72 doubling time ≈ 9.0 yrs).
3-Engine Compounding Snowball Over 20 Years (USD 343,800.00 Nominal) 1. INITIAL PRINCIPAL USD 10,000.00 Grows to USD 49,300.00 alone 2. MONTHLY DEPOSITS USD 120,000.00 USD 500.00/mo × 240 mos 3. COMPOUND INTEREST +USD 213,800.00 62.2% of ending wealth • ~9.0y double
Graph 2 • Nominal Balance vs. Inflation-Adjusted Purchasing Power Adjusting for 2.5% annual inflation converts USD 343,800.00 nominal into USD 209,800.00 in today's purchasing power.
0 189.1k 378.2k --- Real Value (USD 209,800.00) 41.9k Yr 4 85.9k Yr 8 146.3k Yr 12 229.4k Yr 16 343.8k Yr 20
Graph 3 • Projected Maturity Balance Across Return Rates Shows exponential sensitivity to annual return rate over your investment horizon.
0 287.2k 574.4k 232.6k 5.0% 281.8k 6.5% 343.8k 8.0% 422.3k 9.5% 522.2k 11.0%
Summary: After 20 years, total contributions reach USD 130,000.00 and compound growth reaches USD 213,778.24, for a nominal total of USD 343,778.24.
Summary: Starting with USD 10,000.00 and contributing USD 500.00/month (end of month) at 8% over 20 years grows to USD 343,778.24. Direct contributions account for USD 130,000.00, while compound growth generates USD 213,778.24 (62.2% of the total).
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Year-by-Year Compound Growth Schedule

YearCumulative ContributionsCumulative InterestNominal BalanceInflation-Adjusted (Real)
Year 1USD 16,000.00USD 1,055.00USD 17,055.00USD 16,639.00
Year 2USD 22,000.00USD 2,695.00USD 24,695.00USD 23,506.00
Year 3USD 28,000.00USD 4,970.00USD 32,970.00USD 30,616.00
Year 4USD 34,000.00USD 7,932.00USD 41,932.00USD 37,988.00
Year 5USD 40,000.00USD 11,637.00USD 51,637.00USD 45,639.00
Year 6USD 46,000.00USD 16,148.00USD 62,148.00USD 53,590.00
Year 7USD 52,000.00USD 21,531.00USD 73,531.00USD 61,859.00
Year 8USD 58,000.00USD 27,859.00USD 85,859.00USD 70,468.00
Year 9USD 64,000.00USD 35,210.00USD 99,210.00USD 79,440.00
Year 10USD 70,000.00USD 43,669.00USD 113,669.00USD 88,798.00
Year 11USD 76,000.00USD 53,329.00USD 129,329.00USD 98,567.00
Year 12USD 82,000.00USD 64,288.00USD 146,288.00USD 108,773.00
Year 13USD 88,000.00USD 76,655.00USD 164,655.00USD 119,444.00
Year 14USD 94,000.00USD 90,546.00USD 184,546.00USD 130,608.00
Year 15USD 100,000.00USD 106,088.00USD 206,088.00USD 142,297.00
Year 16USD 106,000.00USD 123,419.00USD 229,419.00USD 154,542.00
Year 17USD 112,000.00USD 142,685.00USD 254,685.00USD 167,378.00
Year 18USD 118,000.00USD 164,049.00USD 282,049.00USD 180,840.00
Year 19USD 124,000.00USD 187,684.00USD 311,684.00USD 194,967.00
Year 20USD 130,000.00USD 213,778.00USD 343,778.00USD 209,798.00

Formula & Mathematical Methodology: Compound Growth with Periodic Contributions & Effective Rate Conversion

reff = (1 + rm)m − 1,   rmo = (1 + reff)112 − 1
FV = P(1 + rmo)12t + PMT · [(1 + rmo)12t − 1rmo]
r_eff_annual = (1 + r / m)^m − 1; r_mo = (1 + r_eff_annual)^(1/12) − 1; FV = P(1+r_mo)^(12t) + PMT × [((1+r_mo)^(12t) − 1) / r_mo]
  • P: Initial lump-sum investment
  • PMT: Monthly recurring deposit
  • r: Nominal annual interest rate (decimal)
  • m: Compounding periods per year (1, 4, 12, or 365)
  • t: Investment horizon in years

Rounding: Compounding uses exact effective monthly conversion from the chosen nominal compounding frequency; currency values round to nearest cent/dollar.

Worked Example: $10,000 Initial + $500/Month at 8% Compounded Monthly for 20 Years

An investor starts with $10,000 and contributes $500 at the end of every month for 20 years (240 months) at an 8% nominal rate compounded monthly.

  1. Initial $10,000 compounds over 240 months to $10,000 × (1.006667)^240 = $49,268.03.
  2. 240 monthly contributions of $500 ($120,000 total) compound to $294,510.21.
  3. Combined nominal ending balance = $49,268.03 + $294,510.21 = $343,778.24 ($130,000 contributed + $213,778.24 interest).
Result: Ending nominal balance is $343,778.24, or $209,798.58 in today’s dollars after 2.5% annual inflation.

Frequently Asked Questions

Why does beginning-of-month vs. end-of-month contribution timing change the result?

Depositing at the beginning of each month (an annuity due) gives every monthly contribution one extra month of compounding compared to end-of-month deposits.

What is the difference between nominal balance and inflation-adjusted value?

The nominal balance is the actual dollar figure on your future statement. The inflation-adjusted value divides that future balance by (1 + inflation)^years to show what that money can buy in today’s prices.

Finance & Investing · Savings & Wealth Accumulation

Compound Interest Calculator: inputs, method, and how to read the result

Project nominal and inflation-adjusted investment growth with customizable compounding frequency and deposit timing.

Choose inputs for the case you are checking

The defaults are illustrative. Replace them with values for your case and keep the units shown beside each field.

  • Display Currency: Amounts are treated in the selected currency; no foreign-exchange conversion is applied.
  • Initial Investment Principal: Starting lump-sum deposit at Day 0.
  • Monthly Contribution: Recurring amount added every month.
  • Nominal Annual Return Rate: Expected annual rate before inflation.

What the calculation includes

With the default values shown, Projected Future Balance (Nominal) is USD 343,778.24. The calculation follows Compound Growth with Periodic Contributions & Effective Rate Conversion; the formula and variable definitions above show how the inputs combine.

One-input check: With the other defaults held constant, changing Initial Investment Principal from 10,000 USD ($) to 11,000 USD ($) changes Projected Future Balance (Nominal) from USD 343,778.24 to USD 348,705.04. This is a comparison inside the calculator's stated model, not a prediction.

Where to use caution

  • Converts the selected compounding frequency (daily, quarterly, annual) into an exact equivalent monthly rate so monthly contributions compound consistently.
  • Does not deduct annual capital gains or dividend taxes during the accumulation phase.

Scope: Global Check the assumptions and limitations against your situation before relying on the estimate.

More in Finance & Investing: SIP Calculator (Systematic Investment Plan), CAGR & FIRE Calculator (Financial Independence), PPF Calculator (Public Provident Fund).