30-Year Fixed Loan Rate Comparison Calculator

This calculator compares the monthly principal-and-interest payment and total interest for two 30-year fixed-rate loan scenarios. Enter the same loan amount and two annual APRs to see how the payment and interest differ; get each actual rate and loan estimate from the lender.

Formula

The fixed monthly payment is calculated using the standard amortizing-loan formula: M = P × r ÷ [1 − (1 + r)⁻ⁿ]. Here, M is the monthly principal-and-interest payment in dollars, P is the loan amount in dollars, r is the monthly interest rate as a decimal, and n is the number of monthly payments.

For each scenario, r equals APR ÷ 1,200, converting an annual percentage rate into a monthly decimal rate. The term is fixed at 30 years, so n = 30 × 12 = 360 payments. Scenario A uses its own APR to calculate M_A; Scenario B uses its APR to calculate M_B. The payment difference is M_B − M_A, and the interest difference is that payment difference multiplied by 360. Because both scenarios use the same principal and term, the principal cancels when comparing total interest.

Worked Example

Using the calculator’s default inputs: loan amount P = $300,000, Scenario A APR = 6.5%, Scenario B APR = 7%, and n = 360.

For A, r = 6.5 ÷ 1,200 = 0.0054166667. Substituting gives M_A = 300,000 × 0.0054166667 ÷ [1 − (1.0054166667)⁻³⁶⁰] = $1,896.20 per month, rounded to cents.

For B, r = 7 ÷ 1,200 = 0.0058333333. Substitution gives M_B = 300,000 × 0.0058333333 ÷ [1 − (1.0058333333)⁻³⁶⁰] = $1,995.91 per month, rounded to cents.

Payment difference: $1,995.91 − $1,896.20 = $99.71 per month. Interest difference: $99.71 × 360 = $35,895.60 over the scheduled payments. These figures use the rounded monthly payments, as the calculator does.

Assumptions

• The interest rate stays fixed for the entire 30-year term.
• Payments are monthly, made at the end of each period, with the first payment one month after borrowing.
• Interest accrues monthly at APR divided by 12; the formula treats the entered APR as a nominal annual rate.
• The calculation includes principal and interest only. It excludes lender fees, taxes, homeowners insurance, mortgage insurance, escrow, and any other charges.

How to Use This List

This is a comparison calculator, not a live rate listing. Enter the same proposed principal in both cases, then enter the APRs quoted for the same loan type and term. APR can incorporate certain loan costs, while a note rate may not; check each lender’s quote to confirm exactly what its figure represents. Do not compare one lender’s APR with another lender’s note rate as though they were identical.

The output isolates the effect of the two entered rates on scheduled principal-and-interest payments. A positive payment difference means Scenario B’s payment is higher; a negative result means it is lower. The interest difference uses the same sign convention. A zero difference means the modeled payments match. The comparison does not establish which offer has lower overall costs: fees, points, closing costs, and the time you expect to keep the loan can alter that assessment.

For a like-for-like comparison, use the same loan amount, 30-year fixed term, and similar fee assumptions, and request written loan estimates for the same transaction details. If an offer has a different term, adjustable rate, discount points, or financed fees, this tool does not model those differences. You can use the calculator to test an APR supplied by a lender, but it does not find or predict market rates.

Monthly payment is rounded to the nearest cent, and the interest difference is based on that rounded payment over 360 installments. Actual statements can differ because of payment dates, rounding practices, servicing adjustments, or loan features. The displayed principal-and-interest payment is not the full monthly housing cost.

Frequently Asked Questions

What does a 30-year fixed loan mean?
A 30-year term schedules 360 monthly payments, and a fixed rate remains unchanged under the calculator’s assumptions.

Does APR equal the interest rate?
Not necessarily. APR is a standardized annualized cost measure that may include certain fees; ask the lender what charges its quote includes.

Does the result include property taxes or insurance?
No. It estimates principal and interest only, not taxes, homeowners insurance, mortgage insurance, or escrow.

Why might my lender’s payment differ?
The actual loan amount, rate, fees, payment date, rounding, or loan structure may differ from the inputs and assumptions here.

Can I use this to compare a 15-year loan?
No. This version fixes the term at 30 years. A different term requires recalculating with its own number of payments.

Final Thoughts

Use the two scenarios to understand how APR changes scheduled payments and modeled interest when the amount and term stay constant. Treat the output as estimate arithmetic, not financial advice; the lender’s disclosure gives the exact figures.

Related

• Accrued Interest Account: Asset or Liability?
• Unpaid Accrued Interest Student Loan Calculator
• Student Loan Accrued Interest Calculator and Formula

in p | Loan amount | $ | 300000 | 1 | 100000000
in r1 | Scenario A APR | % | 6.5 | 0.01 | 100
in r2 | Scenario B APR | % | 7 | 0.01 | 100
out paya | Scenario A monthly payment | $ | round(p * (r1 / 1200) / (1 - (1 + r1 / 1200) ^ -360), 2) | 2
out payb | Scenario B monthly payment | $ | round(p * (r2 / 1200) / (1 - (1 + r2 / 1200) ^ -360), 2) | 2
out dif | Payment difference, B minus A | $ | payb - paya | 2
out intd | Interest difference, B minus A | $ | (payb - paya) * 360 | 2