What you can calculate in this section
Calculate simple interest, compound growth, rates, future value and doubling time. Start with the result you need, then confirm that every input comes from the same period and uses the definition shown on the selected page.
A calculator returns a mathematical result. The worked example and limitations explain whether that result belongs in the decision you are making.
13 guides and calculators
Each page below gives the direct definition first, then the equation or method, inputs, sample calculation, common mistakes and related formulas.
Compound Interest Formula
compound interest formula explained with the formula, inputs, example and limitations.
Open Compound Interest Formula →Investment Growth Calculator
investment growth calculator explained with the formula, inputs, example and limitations.
Open Investment Growth Calculator →Simple Interest Formula
simple interest formula explained with the formula, inputs, example and limitations.
Open Simple Interest Formula →Interest Calculator Savings
interest calculator savings explained with the formula, inputs, example and limitations.
Open Interest Calculator Savings →Continuous Compound Interest Formula
continuous compound interest formula explained with the formula, inputs, example and limitations.
Open Continuous Compound Interest Formula →Simple Interest vs Compound Interest
simple interest vs compound interest explained with the formula, inputs, example and limitations.
Open Simple Interest vs Compound Interest →How to Calculate Interest Rate Per Month
how to calculate interest rate per month explained with the formula, inputs, example and limitations.
Open How to Calculate Interest Rate Per Month →Doubling Time Formula
doubling time formula explained with the formula, inputs, example and limitations.
Open Doubling Time Formula →Principal and Interest
principal and interest explained with the formula, inputs, example and limitations.
Open Principal and Interest →Simple Interest Loan Calculator
simple interest loan calculator explained with the formula, inputs, example and limitations.
Open Simple Interest Loan Calculator →Compound Interest Formula Excel
compound interest formula excel explained with the formula, inputs, example and limitations.
Open Compound Interest Formula Excel →Financial Interest Definition
financial interest definition explained with the formula, inputs, example and limitations.
Open Financial Interest Definition →Interest Definition Finance
interest definition finance explained with the formula, inputs, example and limitations.
Open Interest Definition Finance →How to choose the right formula
- Name the decision.
Decide whether you need a value, rate, margin, return, balance or comparison. - Match the timing.
Use annual figures with annual figures and distinguish a point-in-time balance from a period flow. - Check the definition.
Confirm what each numerator, denominator, cash flow or cost includes. - Run an example.
Reproduce the sample result before entering your own figures. - Test another case.
Change one assumption at a time and record what drives the answer.
Frequently asked questions
What is interest and time-value formulas?
Calculate simple interest, compound growth, rates, future value and doubling time.
How should I use interest and time-value formulas?
Use the formula only after matching every input to the same period, unit and definition. Then compare the result with a worked example and the decision you are trying to make.
What is the most common mistake with interest and time-value formulas?
The most common mistake is choosing a familiar formula before defining the decision, period, units and available inputs.
Can I calculate interest and time-value formulas in a spreadsheet?
Yes. Reproduce the displayed equation with separate cells for each input, keep percentages as decimals, and test the spreadsheet against the worked example before replacing the sample figures.
Sources and methodology
The section’s financial context is checked against Investor.gov Compound Interest Calculator. Each leaf page names the source used for its specific formula or reporting relationship.