Loan Comparison Calculator
Compare two loan offers side by side — monthly payment, total interest and total cost.
How this is calculated
Each loan's fixed monthly payment is calculated from its principal, rate and term using the standard amortization formula, then run forward month by month — each payment splits between interest on the remaining balance and principal repayment. Comparing total cost (all payments summed) rather than just the monthly payment is the fairest way to judge two offers with different terms.
The term length alone can make a big difference. A $30,000 loan at 6% over 3 years (36 months) costs about $912/month with roughly $2,848 in total interest. The same $30,000 at the same 6% rate over 5 years (60 months) drops the payment to about $580/month — but total interest rises to roughly $4,796, about $1,948 more, purely from stretching the same loan over a longer term. A lower monthly payment can look more affordable while quietly costing significantly more overall. For the full amortisation schedule on a single mortgage, see the Mortgage Calculator, and to see how paying down debt fits into your overall financial position, see the Net Worth calculator.
Frequently asked questions
- Why compare by total cost instead of monthly payment?
- A lower monthly payment often just means a longer term — which can mean paying more in total interest over the life of the loan. Total cost (all payments added up) is the fairest single number for comparing two loans with different terms.
- What if the two loans have different terms?
- That's exactly what this tool is for — a shorter, higher-payment loan and a longer, lower-payment loan can be compared directly on total interest and total cost, not just the monthly number.
- How is the amortization schedule calculated?
- Each month, interest is charged on the remaining balance at that loan's rate, and the rest of the fixed payment reduces the principal — the same standard amortization method used for mortgages and auto loans.
- Can I use this in my own app?
- Yes — every calculator on Stupidly Clever has a matching REST API and MCP tool that runs the same underlying logic.
- What is APR and how does it differ from the interest rate?
- The stated interest rate reflects only the cost of borrowing on the outstanding balance. APR (Annual Percentage Rate) is a broader figure that also folds in certain fees and charges associated with the loan, giving a more complete picture of the loan's true annual cost — always compare APRs, not just headline interest rates, when shopping for a loan.
- How does loan term affect total interest paid?
- A longer term lowers the monthly payment but increases total interest paid, since the balance takes longer to pay down and accrues interest for more months. A shorter term raises the monthly payment but reduces total interest — the trade-off this calculator is built to compare directly.
- Is it better to pay off early or invest the difference?
- It depends on the loan's interest rate versus your realistic investment return. If your loan rate is lower than what you could reasonably expect to earn investing, paying the minimum and investing the difference can come out ahead financially — though paying off debt also has a guaranteed, risk-free return equal to the interest rate, which many people value for its certainty and peace of mind.