Compound Interest Calculator

Compound growth begins with a principal amount. At each compounding period, interest is calculated from the balance at that point. When interest remains in the balance, a later period can calculate interest on the original principal and prior credited interest. The standard no-deposit form is A = P(1 + r/n)^nt, where P is principal, r is annual rate as a decimal, n is periods per year, and t is years.

This calculator makes the other inputs visible: time, frequency, monthly deposits, whether a deposit arrives at the start or end of the month, and an optional annual increase in contributions. It is not a rate quote, account statement, or forecast.

For a principal of $1,000 at 6% annual rate compounded annually for two years, the calculation is $1,000 × (1 + 0.06)² = $1,123.60. The $123.60 is the modeled interest. If the same rate, time, and principal were modeled with a different compounding frequency, the arithmetic would change because the periodic rate and count of periods are different.

With monthly deposits, a single formula line is less transparent because the balance changes each month. The calculator simulates those deposits under your selected timing. That is why an end-of-month deposit and a start-of-month deposit can produce slightly different outputs under the same annual rate.

A nominal annual rate and an annual percentage yield are related but not interchangeable labels. A stated APY incorporates the effect of a stated compounding arrangement over a year; a nominal rate needs its compounding frequency to determine the effective annual result. This calculator shows the mathematical conversion for the values you enter, but it cannot tell you which disclosure applies to a bank or investment product.

Before using a product’s rate in a scenario, confirm whether the provider states a nominal rate or APY, how often interest compounds or credits, whether the rate can change, whether balances have tiers, and whether withdrawals or fees affect earnings. Those contract terms belong to the provider’s current disclosure.

The page separates total contributions from modeled interest so you can see the source of the final balance. If you deposit $100 every month, the total contributed amount rises even if the return assumption is 0%. A higher final value may therefore come from deposits, modeled growth, or both. Do not compare final balances without first checking that contribution totals and timelines match.

Use the Savings Goal Calculator when the question is “what monthly deposit reaches a named goal by a chosen date?” Use the Investment Calculator when you want to test a broader investment scenario with sensitivity and inflation assumptions. The inputs must still be explicit in either tool.

Simple interest calculates interest from the original principal without adding prior interest to the base: I = P × r × t. The Compound Interest Calculator can show a mathematical comparison, but that does not tell you whether a particular loan, certificate, savings account, or investment uses one method or another. Read the applicable agreement.

For a focused formula check, visit the Simple Interest Calculator. If you are evaluating a certificate of deposit, use the CD Calculator only after checking the issuer’s current APY, term, compounding, maturity, renewal, and early-withdrawal disclosures.

A rate can be advertised, quoted, credited, or calculated on different time bases. Before entering it, note whether the source calls it an annual rate, a periodic rate, an APY, or something else. Then choose the compounding setting that the disclosure actually states. A mathematically correct calculation with a mismatched label is still the wrong scenario for the product.

Keep deposits separate from interest in your records. If you increase a contribution each year, write down the change date and amount. The calculator can apply an annual increase mechanically, but it cannot know whether the additional cash will be available or whether another goal must take priority. Revisit the scenario after a rate or contribution changes.