Calculate
Simple interest assumptions
SIThe reference page solves one simple-interest variable at a time after submit. This version keeps the same four questions on one page and updates the answer, breakdown, and schedule live.
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Finance calculator
Simple Interest Calculator
Use a simple interest calculator to solve end balance, principal, term, or rate with live updates, then review how much of the ending total comes from the original principal versus simple interest.
How to use this calculator
What simple interest means
Interest can be the cost of borrowing money or the compensation earned for lending it. Simple interest is the version that only uses the original principal when calculating interest. That means interest does not compound on earlier interest. The core relationship is straightforward: simple interest equals principal multiplied by rate and time.
- Use yearly mode when the rate is quoted per year and the term is expressed in years.
- Use monthly mode when the rate is quoted per month and the term is counted in months.
- Simple interest grows linearly, so each period adds the same amount of interest instead of compounding on prior gains or charges.
Formula / method
Formula / method
Simple interest is based only on the original principal, not on previously earned interest. That makes the core relationship straightforward and easy to audit.
- The classic formula is I = P × r × t.
- Ending balance equals principal plus simple interest.
- Different time units are normalized into a comparable rate-and-term view.
Example calculation
Review the current live example
The example below reflects the current values shown in the calculator above, so it updates as you change the form without altering the calculation logic itself.
Example inputs
Principal20,000
Rate and term basisInterest rate per year + term in years
Interest rate per year (%)3
Term in years10
Example outputs
Solved fieldEnd balance
Solved value$26,000.00
Principal$20,000.00
Total interest$6,000.00
Disclaimer
Use results as planning guidance only
Results are for reference only and do not constitute financial, investment, tax, or legal advice. Product terms, lender rules, tax treatment, and fees can vary in real situations.
- Do not treat calculator output as financial, investment, medical, or legal advice.
- Check assumptions, dates, tax rules, and provider-specific terms before acting on a result.
- Use official documents or professional guidance when the decision has material consequences.
FAQ
Common Simple Interest questions
What is the simple interest formula?
The standard simple-interest formula is I = P × r × t, where P is principal, r is the rate, and t is the time period. The ending balance is principal plus total interest.
What is the difference between simple interest and compound interest?
Simple interest is calculated only on the original principal. Compound interest adds interest to the balance and then calculates future interest on both principal and previously earned or charged interest.
When is simple interest commonly used?
Simple interest can appear in short-term loans, some bonds, and straightforward return or financing examples where the interest is based only on the starting principal.