Personal Loan Calculator
Calculate monthly payments and total interest for a personal loan. Compare different rates and terms to find the best deal.
This calculator computes the fixed Monthly Payment for a fully amortizing personal loan using the standard amortization formula (lines 14-16): payment equals Loan Amount times the monthly rate times (1 + monthly rate) raised to the number of payments, divided by that same power minus one. If Interest Rate is entered as exactly 0%, the formula switches to a separate branch (lines 11-12) that simply divides Loan Amount by the number of payments — an exact-equality check, not an approximation, so a 0.01% rate still runs through the compounding formula while a literal 0% does not. Loan Amount dominates Monthly Payment: set it 10% below its default, then 10% above, and Monthly Payment swings by exactly 20% end to end, ahead of Loan Term (about 17% over that same range, moving the payment in the opposite direction — a longer term spreads the same principal over more payments) and Interest Rate (about 3%, the smallest mover at these defaults because 10.5% compounded monthly over a 3-year term is still a modest multiplier). Total Interest, by contrast, responds to all three inputs by nearly the same amount: Interest Rate (about 21%), Loan Term (about 20%), and Loan Amount (exactly 20%) sit close enough together that no single input clearly dominates the total interest cost, since term and rate both compound through the same exponent in the amortization formula. This calculator does not account for origination fees, prepayment penalties, or how a borrower's credit profile affects the rate a lender actually offers — Interest Rate is a plain input here, not something the calculator estimates on its own.
Financial Disclaimer
This calculator is for educational purposes only and does not constitute financial advice. Results are estimates based on the inputs provided. Consult a qualified financial advisor before making investment or financial planning decisions.
Inputs
Results
Monthly Payment
$487.54
≈ 9 tanks of gas
Amortising loan payment
- 1.Convert the annual rate to a monthly rate
Payments are monthly, so every term in the formula has to be expressed per month.
- 2.Count the payments
The number of monthly payments over the whole term.
- 3.Solve for the level payment
This comes from setting the present value of all n equal payments equal to the amount borrowed, then solving for the payment. The (1+i)ⁿ − 1 in the denominator is the sum of a geometric series — the same series that drains a pension or decays a drug in plasma, which is why one formula family serves calculators across several hubs.
Simon Stevin published the first printed interest tables, including the present value of an annuity — the relationship this payment formula inverts. Until then such tables were guarded as trade secrets by lenders.
How to Use This Calculator
- Enter the loan amount you need.
- Set the interest rate from your lender's offer (personal loan rates typically range 6-36% APR).
- Enter the loan term in years.
- Review the monthly payment, total payment over the life of the loan, and total interest cost.
- Compare multiple offers by changing the rate and term to find the best overall deal.
How the result changes with Loan Amount
| Loan Amount | Monthly Payment |
|---|---|
| $10,450.00 | $339.65 |
| $35,325.00 | $1,148.15 |
| $65,175.00 | $2,118.35 |
| $90,050.00 | $2,926.85 |
What each input means
- Loan Amount
- Total amount borrowed.
- Interest Rate
- Annual interest rate as a percentage.
- Loan Term
- Length of the loan in the specified time unit.
How this is calculated
Worked example, using the default values
- Identify Input ParametersLoan Amount = 15000, Interest Rate = 10.5, Loan Term = 3 = 3 input(s) provided
- Calculate Monthly PaymentMonthly Payment487.54 = $487.54
- Calculate Total PaymentTotal Payment17551.32 = $17,551.32
- Calculate Total InterestTotal Interest2551.32 = $2,551.32
Engine last updated .
Frequently Asked Questions
What has the biggest effect on the monthly payment?
Loan Amount, by a clear margin — set it 10% below its default, then 10% above, and Monthly Payment swings by exactly 20% end to end, versus about 17% for Loan Term and only about 3% for Interest Rate at the default 10.5% rate and 3-year term. Interest Rate matters more at higher rates or longer terms, but at these defaults its effect on the monthly figure is the smallest of the three.
Does one input dominate the total interest cost the way it dominates the monthly payment?
No single input clearly dominates. Interest Rate, Loan Term, and Loan Amount each move Total Interest by a similar amount across a ±10% probe — roughly 21%, 20%, and 20% respectively — because Total Interest depends on rate and term through the same compounding exponent in the amortization formula (lines 14-16), not through one dominant factor.
What happens to the payment formula if I set the interest rate to exactly 0%?
The engine switches formulas entirely rather than approximating. At exactly 0% (line 11's monthlyRate === 0 check), Monthly Payment becomes simply Loan Amount divided by the number of payments, with no interest component at all. Any rate above 0%, even 0.01%, instead runs through the full compounding amortization formula on lines 14-16.
Does a longer loan term always raise or lower the monthly payment?
Yes — Loan Term and Monthly Payment move in opposite directions: stretching the term from 3 years toward the calculator's 10-year maximum spreads the same Loan Amount over more payments and lowers each one, while shortening it raises the payment. A one-sided 10% increase in Loan Term alone (3 years to 3.3 years) lowers Monthly Payment by about 8% at the defaults ($487.54 to $449.83); the 17% figure elsewhere describes the full two-sided swing across a ±10% probe (3.3 years versus 2.7 years), not the effect of a single 10% increase.
Shares mathematics with
These calculators are built on the same formula — Amortising loan payment, across different categories.
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