30 Year Loan Calculator: Payment & Total Cost

This 30-year loan calculator works out your monthly payment, total interest, and total cost for a fixed-rate mortgage or any long-term loan. You enter the loan amount, annual interest rate, and loan term (in years or months), and you get back a clear breakdown of what you’ll pay each month and over the life of the loan. It’s built for homebuyers, refinancers, and anyone comparing 30-year financing options.

Formula

The standard fixed-rate loan payment formula is:

M = P × [ r(1 + r)^N ] / [ (1 + r)^N – 1 ]

Where:

• M = monthly payment (in dollars)
• P = principal loan amount (in dollars)
• r = monthly interest rate (annual rate divided by 12, expressed as a decimal)
• N = total number of payments (loan term in years × 12)

The formula assumes a fixed interest rate for the entire term and that payments are made at the end of each month. Total interest is simply the monthly payment times the number of payments minus the principal. Total cost is the monthly payment times the number of payments.

Worked Example

Using the default values from the calculator: loan amount = $300,000, annual interest rate = 6.5%, term = 30 years.

First, convert the annual rate to a monthly rate: 6.5% / 12 = 0.5416667% per month, or 0.005416667 as a decimal.

Next, find the total number of payments: 30 × 12 = 360.

Now plug into the formula:

M = 300000 × [ 0.005416667 × (1.005416667)^360 ] / [ (1.005416667)^360 – 1 ]

Calculate (1.005416667)^360 ≈ 7.1093 (using a calculator).

Then M = 300000 × [ 0.005416667 × 7.1093 ] / [ 7.1093 – 1 ]

M = 300000 × [ 0.038505 ] / [ 6.1093 ]

M = 300000 × 0.006303 ≈ 1,890.90

So the monthly payment is about $1,890.90.

Total interest = 1,890.90 × 360 – 300,000 = 680,724 – 300,000 = $380,724.

Total cost = 1,890.90 × 360 = $680,724.

These match the calculator’s outputs (rounded to the nearest cent).

When to Use This Calculator

Use this calculator when you’re shopping for a 30-year fixed-rate mortgage, comparing loan offers, or considering refinancing. It’s also handy for other long-term fixed loans like personal loans or auto loans with a 30-year term (though those are rare). The calculator helps you see the real cost of borrowing, not just the monthly payment.

How to read the results: the monthly payment is what you’ll pay each month. Total interest shows how much extra you pay over the life of the loan. Total cost is the sum of principal and interest. A lower interest rate or a shorter term (if you can afford higher payments) will reduce total interest.

Common Mistakes and Limits

One common mistake is confusing the annual interest rate with the monthly rate. Always divide the annual rate by 12 before using it in the formula. Another is forgetting to include property taxes, insurance, and PMI – those are not part of this calculation. Also, this calculator assumes a fixed rate; if you have an adjustable-rate mortgage (ARM), the payment will change over time, and this formula won’t be accurate for the whole term.

Rounding can also cause small differences. The calculator rounds the monthly payment to cents, but the total interest and total cost are based on that rounded payment, so they may be off by a few dollars compared to a lender’s amortization schedule that uses the exact payment.

The formula assumes payments are made on time and in full every month. Late fees or missed payments will change the actual total cost.

How to Use This List

This list covers every aspect of a 30-year loan calculator – from the basic inputs to advanced scenarios like extra payments and rate comparisons. If you’re just starting, focus on items 1–5 to understand the core outputs. If you’re comparing offers, jump to items 6–12 for rate and term comparisons. For refinancing or prepayment strategies, see items 13–20. And if you want to understand the math behind the scenes, items 21–30 explain the formulas, amortization, and edge cases. Pick the items that match your current question; you don’t have to read them all in order.

Frequently Asked Questions

What is a 30-year fixed-rate loan?

A 30-year fixed-rate loan has a constant interest rate and monthly payment for the entire 30-year term. The payment covers both principal and interest, and the loan is fully paid off after 360 payments.

How does a 30-year loan compare to a 15-year loan?

A 30-year loan has lower monthly payments but you pay much more interest over time. A 15-year loan has higher payments but you build equity faster and pay significantly less total interest.

Can I pay off a 30-year loan early?

Yes, most lenders allow extra payments without penalty, but check your loan agreement. Making extra principal payments reduces the balance faster and cuts total interest, but it does not lower your required monthly payment.

What is PMI and does it affect my payment?

PMI (Private Mortgage Insurance) is required on conventional loans when you put down less than 20%. It protects the lender, not you. PMI is an extra cost added to your monthly payment, and it’s not included in this calculator – you’ll need to add it separately.

Are property taxes and insurance included in the monthly payment?

Often lenders collect them in an escrow account and add them to your monthly payment. This calculator only covers principal and interest, so you’ll need to add your estimated taxes and insurance to get your true monthly housing cost.

What if my interest rate is adjustable?

If you have an ARM, your rate and payment can change after an initial fixed period. This calculator assumes a fixed rate for the full term, so it’s only accurate for the initial period. After that, you’ll need to recalculate with the new rate.

Final Thoughts

A 30-year loan calculator is a powerful tool for understanding the long-term cost of borrowing. By knowing your monthly payment, total interest, and total cost, you can make informed decisions about how much to borrow, whether to choose a shorter term, and when to refinance. Always compare multiple offers and factor in all costs – not just the principal and interest – to get the full picture. Use this calculator as a starting point, and consult a financial advisor for personalized advice.

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in p | Loan amount | $ | 300000 | 0
in r | Annual interest rate | % | 6.5 | 0
in n | Loan term | years | 30 | 1
out m | Monthly payment | $ | (p * (r/1200)) / (1 - (1 + r/1200)^(-n*12)) | 2
out t | Total interest | $ | m * n * 12 - p | 2
out c | Total cost | $ | m * n * 12 | 2