Interest Calculator
Simple and compound interest.
Inputs
$
%
Result
Simple Interest$5,000.00
Compound Interest$6,288.95
About the Interest Calculator
The Interest Calculator computes how much interest a starting principal will earn over time, with optional monthly contributions, so you can plan savings or investment growth.
Calculation method
Same compound-interest formula used by the Compound Interest Calculator, defaulting to monthly compounding.
FV = P(1+r)^n + PMT × ((1+r)^n − 1)/rHow to use this calculator
- Enter the starting amount and any recurring monthly deposit.
- Enter the annual rate and number of years.
- See total interest and final balance.
Example
$25,000 at 5% for 10 years, no additional deposits, grows to about $41,200 — $16,200 in interest.
Frequently asked questions
Is this pre-tax or post-tax?
Pre-tax. Interest from savings accounts, CDs, and bonds is generally taxed as ordinary income; adjust the rate down by your marginal tax bracket for after-tax growth.
What compounds better — monthly or daily?
Daily compounding yields slightly more, but on typical rates the difference is only a few dollars per $10,000 per year.
Does inflation change the result?
Yes. Subtract your inflation assumption (2–3%) from the interest rate to see real growth in today's dollars.
Student loans: what to know before you calculate
Student loans are amortizing installment loans — the same math as auto and personal loans — but the terms, rates, and repayment plans are unique. US federal loans have fixed rates set each July, standard 10-year terms, and income-driven options. Private loans price on credit and can be fixed or variable. Whichever type you have, the monthly payment depends on three inputs: balance, interest rate, and term.
Worked examples
- Undergraduate — $27,000 federal
$27,000 balance at 6.53% on the Standard 10-year plan = about $307/month, with roughly $9,850 total interest over the life of the loan.
- Graduate — $60,000 federal
$60,000 balance at 8.08% on a 10-year term = about $730/month, with roughly $27,600 total interest paid.
- Refinance — $45,000 private
Refinancing $45,000 from 7.5% to 5.75% over 10 years drops the payment from $534 to $493 and saves close to $5,000 in interest — if you don't need federal protections.
Student loan FAQs
How is a student loan monthly payment calculated?
Student loans use the standard amortizing-loan formula: M = P × r × (1 + r)^n / ((1 + r)^n − 1), where P is the balance, r is the monthly interest rate (APR ÷ 12), and n is the number of months. Federal loans typically use a 10-year (120-month) standard term.
What is a realistic interest rate for student loans?
US federal undergraduate Direct loans for 2024–25 are 6.53% fixed, graduate Direct loans 8.08%, and PLUS loans 9.08%. Private student loan rates typically range from 4% to 15% depending on credit and whether you choose fixed or variable.
Standard vs. income-driven repayment — which saves more?
The Standard 10-year plan has the highest monthly payment but the lowest total interest. Income-driven plans (SAVE, IBR, PAYE) lower payments based on income but extend the term to 20–25 years, so total interest paid is usually much higher unless forgiveness applies.
Should I refinance federal student loans?
Refinancing to a private lender can reduce your rate if you have strong credit and stable income, but it permanently forfeits federal benefits: income-driven plans, deferment, forbearance, and Public Service Loan Forgiveness (PSLF). Only refinance federal loans if you're certain you won't need those protections.
Do extra payments really shorten a student loan?
Yes. Every extra dollar goes to principal, which lowers the balance interest is charged on next month. Just $50 extra per month on a $30,000 loan at 6% over 10 years pays it off about 18 months early and saves roughly $1,600 in interest.
Ready to run the numbers?
Use the dedicated Student Loan Calculator to see your monthly payment and total interest.
Disclaimer: This calculator is for informational and educational purposes only and does not constitute financial, tax, or legal advice. Consult a qualified professional for decisions specific to your situation.