How to use the compound interest calculator
Start by choosing Simple Interest, Compound Interest, APY (Effective Yield), or APR (Borrowing Cost). Enter the values shown for that mode, then click Calculate. The Result section shows the formula, assumptions, and any growth or payment schedule the mode supports.
- Select a mode: Simple Interest, Compound Interest, APY (Effective Yield), or APR (Borrowing Cost).
- Enter the displayed inputs, including Term unit and the frequency used by the selected mode.
- In Simple Interest or Compound Interest, set Solve for to Future value, Principal, Rate, or Time when that value is missing.
- Click Calculate and review Result, including the formula, assumptions, and schedule.
Inputs for each calculator mode
Simple Interest applies interest to the original Principal ($). Compound Interest adds interest after each selected Compounding frequency. APY (Effective Yield) calculates an effective annual yield from Nominal annual rate (%) and Compounding frequency; Principal ($) and Term are optional inputs for a dollar projection. APR (Borrowing Cost) uses Principal / loan amount ($), Nominal annual rate (%), Term, Payment frequency, and Upfront fees ($, optional).
Principal / loan amount ($): 10000
Nominal annual rate (%): 6.5
Term: 5 Years
Compounding frequency: Monthly (12/year)
Future value: $13,828.17
Total interest: $3,828.17What Solve for changes
In Simple Interest and Compound Interest, the selected Solve for field is cleared and disabled. Future value projects the ending balance. Principal works backward from a target, Rate finds the nominal annual rate, and Time finds the term. Rate and Time require Future value ($) to be greater than Principal ($); Time also requires a rate above 0.
Terms entered in months become fractional years in the formulas. Simple Interest uses yearly schedule rows. Compound Interest and APY use compounding-period rows, while APR uses whole payment periods. Growth and payment schedules display at most 600 rows. APR rejects a term and Payment frequency that create more than 4,800 payment periods.
Input limits and result files
Where required, Principal ($) and Future value ($) must be greater than 0. Nominal annual rate (%) accepts 0 through 100. When entered, Term must be greater than 0. In APR (Borrowing Cost), Upfront fees ($, optional) must be 0 or greater and less than the principal. The formulas use a fixed rate and evenly spaced periods; variable rates, irregular contributions, taxes, and account-specific terms are outside this calculation.
After a calculation, Copy result copies a plain-text summary and Download result (.txt) saves it. The exported text leaves out schedule rows. In APY mode it also leaves out Principal and Term, and in APR mode it leaves out the total of all payments. Reset clears numeric inputs and fees, restores the default selectors, hides Result, and keeps the selected mode.
Compare compounding and quoted rates
To compare monthly and daily compounding, enter the same Principal ($), Nominal annual rate (%), and Term, then change Compounding frequency. Compare the effective annual rate and the schedule rows.
For a target balance, choose Solve for Principal, Rate, or Time. To check a quoted annual yield, select APY (Effective Yield) and compare the effective yield with Nominal annual rate (%).
When another financial calculator fits better
Browse Financial Calculators for loan, investing, pay, housing, debt, or savings calculations. Use APY Calculator for APY from a nominal rate and compounding frequency. Use APR Calculator when loan APR and payment timing are the main results. Choose Amortization Calculator for a loan balance split into principal and interest for each period.
Frequently asked questions
How do I calculate compound interest?
Enter Principal ($), Nominal annual rate (%), Term, Term unit, and Compounding frequency. Select Compound Interest, then click Calculate. The result uses A = P x (1 + r/n)^(n x t) and shows total interest and a period schedule.
Can I calculate compound interest in months?
Enter the number of months in Term and choose Months in Term unit. The formula converts that term to fractional years. The schedule uses a rounded count of compounding periods.
How do I calculate APY from a nominal rate?
Select APY (Effective Yield), enter Nominal annual rate (%) and Compounding frequency, and click Calculate. Add Principal ($) and Term to see a future value and growth schedule.
How does the APR mode handle upfront fees?
APR (Borrowing Cost) subtracts Upfront fees ($, optional) from the net amount financed. It sizes payments from the full Principal / loan amount ($) and Nominal annual rate (%), then solves for the periodic APR that discounts those payments to the net amount financed.