Compound Interest Calculator

Model compound growth with monthly deposits, clear timing, inflation and a downloadable schedule.

Explore an assumption, not a promise. Compare a fixed rate and regular contributions, with clear deposit timing and a year-by-year schedule. This educational estimate is not financial advice or a guaranteed return.

Initial amount

Monthly contribution

Annual nominal rate (%)

Whole years

Extra months (0–11)

Compounding frequency

Monthly contribution timing

Annual inflation assumption (%)

Display currency (no conversion)

Projected balance

31,998.32

Total contributed

22,000.00

Interest / change

9,998.32

Effective annual growth: 5.1162%. After 120 months, inflation-adjusted purchasing power in today's units: 31,998.32. Changing the display currency does not convert amounts.

Year-end snapshots, plus the final partial year. Rounded only for display.
Year / month	Contributed	Interest / change	Balance
1y 0m	11,200.00	539.50	11,739.50
2y 0m	12,400.00	1,168.01	13,568.01
3y 0m	13,600.00	1,890.06	15,490.06
4y 0m	14,800.00	2,710.44	17,510.44
5y 0m	16,000.00	3,634.20	19,634.20
6y 0m	17,200.00	4,666.60	21,866.60
7y 0m	18,400.00	5,813.23	24,213.23
8y 0m	19,600.00	7,079.91	26,679.91
9y 0m	20,800.00	8,472.79	29,272.79
10y 0m	22,000.00	9,998.32	31,998.32

Calculation assumptions and limits

With annual nominal rate r and n compounding periods per year, monthly growth is (1 + r/n)^(n/12) − 1. Each month, the contribution is added either before or after this growth. This equivalent-month model uses fractional compounding periods; a bank's actual crediting and day-count rules may differ.

The rate, contribution and inflation stay constant. Daily compounding assumes 365 periods, not actual calendar dates. No fees, taxes, withdrawals, varying market returns or rounding at each monthly step are included. Negative assumed rates can reduce the balance. Inflation changes purchasing power, not the nominal balance.

Limits: 1–1,200 months, initial amount and monthly contribution up to 1 billion each, nominal rate −99% to 100%, inflation 0%–50%, projected balance up to 1 quadrillion. All calculations and CSV exports stay in this browser; inputs are not sent to a calculator API.

This tool runs entirely in your browser. Your data is never uploaded, never stored, and never leaves your device.

Compare hypothetical compound growth with monthly contributions, explicit deposit timing, inflation-adjusted value and a downloadable year-by-year schedule.

How to use it

1Enter an initial amount, monthly contribution and annual nominal rate.
2Choose duration, compounding frequency and beginning/end-of-month contributions.
3Review contributed money, interest/change, effective annual growth and optional inflation adjustment.
4Download the schedule with its assumptions; use it as an illustration, not advice or a guarantee.

Example

Input: 1,000 initial; 100/month at month end; 12% nominal, compounded monthly; 1 year.
Output: 2,395.08 balance = 2,200.00 contributed + 195.08 interest/change.

Hypothetical fixed-rate illustration; fees and taxes are excluded.

What happens to your data

Projection inputs, calculations and CSV generation remain in your browser. The calculator makes no financial-data API request. Changing a currency changes only the display label, not the amount.

Last updated October 2026

Model a fixed annual nominal rate, an initial amount and monthly contributions. Choose whether contributions arrive at the beginning or end of each month, compare compounding frequencies, and separate contributed money from the projected interest or loss. The schedule shows each year end and a final partial year.

An optional inflation assumption translates the final balance into today's purchasing-power units. Display currencies are labels only: selecting INR rather than USD does not apply an exchange rate. Download the schedule with its rate, timing and calculation assumptions as CSV.

How it works

The model converts the nominal annual rate r and n compounding periods per year into an equivalent monthly growth rate: i = (1 + r/n)^(n/12) − 1. It then applies that monthly rate for the requested whole number of months. For an end-of-month contribution D, the recurrence is B(next) = B × (1+i) + D. For a beginning-of-month contribution, it is B(next) = (B + D) × (1+i). This gives each monthly deposit the appropriate time in the model, rather than pretending a year's contributions all arrived at the start of the year.

Without contributions, the result is the standard P × (1+r/n)^(n×t). For monthly deposits with i not equal to zero, the end-of-month closed form is P(1+i)^m + D((1+i)^m−1)/i; beginning-of-month deposits multiply the deposit term by 1+i. At zero rate, the balance is simply P + D×m. Negative input rates are permitted, so interest/change can be negative.

For compounding frequencies other than monthly, fractional compounding periods are modelled exponentially. This is an explicit comparison convention, not a simulation of a particular bank's posting rules. Daily means 365 equal periods per year; actual calendars, leap days, day counts and institution-specific rounding are not simulated. Calculations retain floating-point precision internally and round only for display and CSV.

Inflation-adjusted balance is nominal balance divided by (1+f)^t, where f is the annual inflation assumption. The model keeps rates, deposits and inflation constant; it excludes taxes, fees, withdrawals and variable market returns. These assumptions can dominate real outcomes. This is an educational estimate, not personalized advice, a product recommendation or a return guarantee.

Inputs accept plain decimal numbers without commas or currency symbols. Duration is 1–1,200 whole months; the initial amount and monthly contribution are each at most 1 billion. Annual nominal rate is −99% to 100%, inflation is 0% to 50%, and projected balances above 1 quadrillion are refused. An invalid input removes the previous projection so it cannot be mistaken for the new scenario. The computation and CSV generation run in the browser without a calculator API request.

Worked example: A small, verifiable monthly savings example

Input: Initial amount 1,000; nominal rate 12%; monthly compounding; 100 deposited at each month end; 1 year; inflation 0%
Result: Contributed: 2,200.00; interest/change: 195.08; projected balance: 2,395.08

The monthly rate is 1%. Beginning-of-month deposits instead produce 2,407.76. These are hypothetical arithmetic results, not a rate forecast.

Common use cases

Seeing how contribution timing changes a fixed-rate illustration
Comparing principal contributions with assumed interest growth
Checking a zero-rate or negative-rate scenario without hiding a loss
Saving a transparent year-by-year scenario with its assumptions

Frequently asked questions

Is the annual nominal rate the same as APY?＋

Not generally. With nominal rate r compounded n times per year, the effective annual rate is (1+r/n)^n−1. This tool expects the nominal rate and shows the effective annual growth separately. Do not paste a quoted APY as a nominal rate unless you intentionally want that different assumption.

Why do different calculators return different amounts?＋

Contribution timing, contribution frequency, rate definitions, fractional-period assumptions, fees and rounding can differ. This tool exposes beginning/end-of-month timing and an equivalent monthly growth convention so you can compare like with like.

Does changing the currency convert my money?＋

No. It changes the display label only. Amounts stay numerically the same and no exchange-rate data is requested. Neutral units are also available.

Can the result tell me what investment to buy?＋

No. It only calculates a constant-rate scenario you enter. Actual investments can lose value and do not follow a smooth guaranteed rate. Fees and taxes are not included.