ganak.appInterest Rate Calculator
Calculate interest rate, monthly payment, loan amount, or loan term for any fixed-rate loan. Find the interest rate you are being charged, see total interest paid, view a year-by-year amortization schedule, and compare how different rates affect your payments. Works for mortgages, car loans, personal loans, and student loans.
Payment Breakdown
Principal vs interest over the life of the loan
Rate Comparison
How different rates affect your payment and total interest
Amortization Schedule
Year-by-year breakdown of principal and interest
| Year | Beginning Balance | Principal | Interest | Ending Balance |
|---|---|---|---|---|
| 1 | $250,000 | $3,066 | $14,934 | $246,934 |
| 2 | $246,934 | $3,255 | $14,745 | $243,679 |
| 3 | $243,679 | $3,456 | $14,544 | $240,222 |
| 4 | $240,222 | $3,670 | $14,330 | $236,552 |
| 5 | $236,552 | $3,896 | $14,104 | $232,656 |
| 6 | $232,656 | $4,137 | $13,863 | $228,519 |
| 7 | $228,519 | $4,393 | $13,607 | $224,126 |
| 8 | $224,126 | $4,664 | $13,336 | $219,463 |
| 9 | $219,463 | $4,952 | $13,048 | $214,511 |
| 10 | $214,511 | $5,258 | $12,742 | $209,253 |
What Is an Interest Rate?
Understanding the cost of borrowing money
An interest rate is the percentage charged by a lender on the outstanding loan balance, expressed annually. It determines how much you pay to borrow money. For savings accounts and CDs, the interest rate represents what the bank pays you for depositing your money.
Interest rates are influenced by central bank policies, inflation expectations, credit risk, and market conditions. Fixed rates stay constant throughout the loan term, while variable rates fluctuate with market benchmarks.
Interest Rate Formulas
The math behind loan payment calculations
Monthly Payment Formula
PMT = P × r / (1 - (1 + r)-n)
Where P = loan principal, r = monthly interest rate (annual rate ÷ 12 ÷ 100), and n = total number of monthly payments.
Finding the Interest Rate
Solved numerically using Newton-Raphson iteration
Unlike payment or loan amount, interest rate cannot be isolated algebraically from the amortization formula. This calculator uses Newton-Raphson numerical methods to find the exact rate that produces your given payment.
How This Calculator Works
Four solve modes for complete flexibility
- Find Interest Rate: Enter loan amount, monthly payment, and term to discover the rate you are being charged.
- Find Monthly Payment: Enter loan amount, interest rate, and term to see your expected monthly obligation.
- Find Loan Amount: Enter payment, rate, and term to learn how much you can afford to borrow.
- Find Loan Term: Enter loan amount, rate, and payment to see how long until payoff.
All modes include a yearly amortization schedule, rate sensitivity analysis, and a balance chart showing how principal and interest change over the life of the loan.
Real World Example
Finding the interest rate on a $25,000 car loan with $480/month payments over 5 years
You took a $25,000 car loan and pay $480 per month for 60 months. What rate are you paying? Using the Find Interest Rate mode, the calculator determines your annual rate is approximately 5.71%. Total payments are $28,800, meaning $3,800 goes to interest over the life of the loan.
Inputs
- Loan amount: $25,000
- Monthly payment: $480
- Loan term: 60 months (5 years)
Outputs
- Annual interest rate: 5.71%
- Total payments: $28,800
- Total interest: $3,800
- Interest-to-loan ratio: 15.2%
Interest Rate vs APR
Understanding the real cost of borrowing
| Factor | Interest Rate | APR |
|---|---|---|
| Includes fees | No | Yes |
| Best for comparing | Monthly cost | Total cost |
| Required by law | No | Yes (TILA) |
| Always higher | - | Yes (or equal) |
Common Mistakes
Errors that lead to underestimating loan costs
Confusing interest rate with APR when comparing loan offers from different lenders.
Focusing only on monthly payment without checking total interest over the full loan term.
Ignoring the impact of even a 0.25-0.5% rate difference, which compounds significantly over long terms.
Not considering that longer loan terms mean lower payments but substantially more total interest paid.
Forgetting that variable rates can increase over time, making initial low rates misleading.
Frequently Asked Questions
Common questions about interest rates, loan payments, and amortization