Loan Calculator

How to Use the Loan Calculator

This calculator handles three loan scenarios: find your monthly payment from a loan amount, find how much you can borrow from a target payment, or find how long it will take to pay off a loan. All calculations use standard amortization formulas with exact decimal arithmetic. Results include charts, amortization schedules, and payoff comparisons.

Calculation Modes

Payment — Find Your Monthly Payment

Enter the loan amount, annual interest rate, and term in years. The calculator computes the fixed monthly payment using standard amortization.

Formula: M = P × [r(1 + r)^n] / [(1 + r)^n − 1]

Where P = principal, r = monthly rate (annual / 12), n = total months (years × 12).

Example: $300,000 home loan at 6% for 30 years

• Loan Amount: 300000
• Interest Rate: 6
• Loan Term: 30
• Monthly Payment: 1,798.6516

Example: $20,000 car loan at 4.5% for 5 years

• Loan Amount: 20000
• Interest Rate: 4.5
• Loan Term: 5
• Monthly Payment: 372.86038

After calculating, a stacked area chart shows how principal (green) and interest (orange) shift over the life of the loan. Early payments are mostly interest; later payments are mostly principal. Below the chart, a paginated amortization schedule breaks down every payment into principal, interest, and remaining balance. The table shows 10 rows per page with navigation controls.

Amount — Find How Much You Can Borrow

Enter your target monthly payment, the interest rate, and the loan term. The calculator computes the maximum loan amount you can afford.

Formula: P = M × [(1 + r)^n − 1] / [r(1 + r)^n]

Example: You can afford $500/month at 4% for 15 years

• Monthly Payment: 500
• Interest Rate: 4
• Loan Term: 15
• Loan Amount: 67,596.074

Example: You can afford $400/month at 3.9% for 6 years

• Monthly Payment: 400
• Interest Rate: 3.9
• Loan Term: 6
• Loan Amount: 25,641.583

A bar chart compares the principal amount (green) against the total interest (orange) over the term. Below the chart, an affordability summary table shows the max loan amount, monthly payment, rate, term, total payments, total interest, and total cost.

Term — Find the Payoff Time

Enter the loan amount, interest rate, and your monthly payment. The calculator computes how many months it will take to pay off the loan and compares it against a standard 30-year term.

Formula: n = −ln(1 − rP/M) / ln(1 + r)

Example: $30,000 personal loan at 5% with $600/month payments

• Loan Amount: 30000
• Interest Rate: 5
• Monthly Payment: 600
• Loan Term: 56 months (4 years 8 months)

Example: $15,000 personal loan at 8% with $350/month payments

• Loan Amount: 15000
• Interest Rate: 8
• Monthly Payment: 350
• Loan Term: 51 months (4 years 3 months)

A bar chart compares your payoff timeline against a standard 30-year term. A payoff timeline table shows your term in years and months, the total cost, and the interest saved versus a 30-year baseline. If your payment is too low to cover the interest, the calculator shows an error.

Precision and Notation Settings

Use the settings bar above the tabs to control how results display:

• Decimal places: Adjust from 0 to 16 decimal places (default is 8)
• Notation: Switch between auto, fixed, exponential, and engineering notation (default is auto)

Your decimal places and notation settings save to your browser automatically. When you return to this calculator, your last chosen format loads without needing to adjust it again.

Common Use Cases

Buying a Home

You are approved for a $350,000 mortgage at 6.25% for 30 years:

1. Switch to Payment
2. Enter 350000 as Loan Amount
3. Enter 6.25 as Interest Rate
4. Enter 30 as Loan Term
5. Monthly Payment: 2,155.0102 (scroll the amortization schedule to see when principal exceeds interest, around payment 228)

Shopping for a Car

The dealer offers 3.9% for 60 months. You want to keep payments under $400:

1. Switch to Amount
2. Enter 400 as Monthly Payment
3. Enter 3.9 as Interest Rate
4. Enter 5 as Loan Term
5. Loan Amount: 21,772.939 (your maximum loan)

Paying Off Debt Faster

You owe $25,000 on a loan at 7% with a $300 minimum payment. How much faster if you pay $500?

1. Switch to Term
2. Enter 25000 as Loan Amount
3. Enter 7 as Interest Rate
4. Enter 500 as Monthly Payment
5. Loan Term: 59 months (4 years 11 months, versus the $300 minimum at approximately 9.5 years)

Refinancing Comparison

You have 25 years left on a $280,000 loan at 6.5%. A lender offers 5.25% with $3,000 in closing costs:

1. Switch to Payment
2. Enter 280000 as Loan Amount
3. Enter 6.5 as Interest Rate
4. Enter 25 as Loan Term
5. Monthly Payment: 1,890.5801 (current loan)

Now calculate the new loan with closing costs added to the principal:

1. Enter 283000 as Loan Amount
2. Enter 5.25 as Interest Rate
3. Enter 25 as Loan Term
4. Monthly Payment: 1,695.871 (new loan with closing costs)
5. Monthly savings: 194.70902. Break-even: approximately 15.4 months

Tips for Accurate Calculations

1. Enter the annual rate, not monthly: The calculator divides by 12 internally. Enter 6 for 6% APR, not 0.5
2. Rates must be positive: 0% uses simple division; negative rates are rejected
3. Payment must exceed monthly interest: In Term mode, a payment below the first month's interest triggers an error
4. Amortization schedules are paginated: Use the page controls to navigate. The footer shows totals
5. Interest saved is vs. a 30-year baseline: The Term mode comparison uses the same amount and rate over 30 years
6. Chart colors are consistent: Green represents principal, orange represents interest across all charts and tables
7. Large loans may display in scientific notation: Switch notation to fixed for comma-separated formatting
8. The amortization table rounds per-payment values: Row totals may differ; footer is exact

Troubleshooting

Required

This appears when a field is left empty. Enter a value in all fields before calculating.

Amount must be positive

Enter a positive principal. Zero or negative amounts are not valid loans.

Rate cannot be negative

Enter a positive annual percentage rate. Zero is accepted in some modes but negative rates are always rejected.

Term must be positive

Enter a positive number of years. Partial years are accepted (e.g., 4.5 for 54 months).

Payment must be positive

Enter a positive payment amount. The payment must be large enough to cover at least the first month's interest.

Payment too low to cover interest

In Term mode, your payment does not cover the interest accrued in the first month. The loan balance would grow instead of shrink. Increase your payment or reduce the amount/rate.

Chart or table not appearing

The details section only renders after a successful calculation with no validation errors. Check that all inputs are filled and valid, then click Calculate.