📚 Formula: M = P[r(1+r)^n]/[(1+r)^n-1] — Standard amortization formula used by all major financial institutions.
How Is a Mortgage Payment Calculated?
A mortgage payment is calculated using the formula M = P[r(1+r)n] / [(1+r)n – 1], where P is the loan amount, r is the monthly interest rate, and n is the total number of payments. This formula ensures each monthly payment is the same amount over the entire loan term.
For example, a $300,000 mortgage at 6.5% annual interest for 30 years has a monthly payment of $1,896.20. The monthly rate is 6.5% / 12 = 0.5417%, and total payments are 30 × 12 = 360. In the early years, most of each payment goes toward interest. Over time, more goes toward reducing the principal balance.
How Much Interest Do You Pay on a 30-Year Mortgage?
On a typical 30-year mortgage, you often pay more in total interest than the original loan amount. A $300,000 loan at 6.5% results in approximately $382,633 in total interest over 30 years — meaning you pay $682,633 total for a $300,000 home.
This is why many financial advisors recommend considering 15-year mortgages when affordable. The same $300,000 at 6.5% over 15 years costs $170,388 in total interest — saving over $212,000 compared to the 30-year term, though the monthly payment is higher at $2,613.32.
How Do Extra Payments Reduce Your Mortgage?
Extra monthly payments go directly toward reducing the loan principal, which lowers total interest and shortens the loan term. Even modest extra payments can save tens of thousands of dollars over the life of a mortgage.
For example, adding just $200 per month to a $300,000 mortgage at 6.5% for 30 years saves approximately $82,000 in interest and pays off the loan roughly 5 years early. Adding $500 per month saves around $155,000 and shortens the term by nearly 10 years. Use this calculator's extra payment feature to see your specific savings.
What Is an Amortization Schedule?
An amortization schedule is a complete table showing how each payment is split between principal and interest over the entire loan term. It reveals the gradual shift from interest-heavy payments at the start to principal-heavy payments at the end.
In the first year of a $300,000 mortgage at 6.5%, approximately $19,354 goes to interest and only $3,401 reduces the principal. By year 25, those proportions reverse: roughly $6,090 goes to interest and $16,665 reduces the principal. This calculator generates a complete yearly amortization schedule automatically with every calculation.
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Disclaimer: This calculator is for educational and informational purposes only. It does not constitute financial advice. Results are estimates based on the inputs provided and do not include property taxes, homeowner's insurance, PMI, or HOA fees. Actual mortgage payments may differ. Consult a qualified financial advisor or mortgage professional before making borrowing decisions.
Mortgage Calculator Guide: How to Calculate Your Monthly Payment and Save Money
A mortgage is likely the largest financial commitment you will ever make. Understanding how mortgage payments work — and how small changes in rate, term, or extra payments can save you tens of thousands of dollars — is essential knowledge for any homebuyer. This calculator uses the standard amortization formula used by every bank and lending institution worldwide.
How Much House Can You Afford?
The general guideline is that your monthly housing payment (including taxes and insurance) should not exceed 28% of your gross monthly income. For a household earning $75,000 per year ($6,250/month), the maximum recommended payment is $1,750. At 6.5% interest for 30 years, this supports a loan of approximately $277,000. Factor in a 20% down payment, and you can afford a home priced around $346,000.
15-Year vs. 30-Year: The Real Cost Difference
On a $300,000 mortgage at 6.5%: a 30-year term costs $1,896/month and $382,633 in total interest. A 15-year term costs $2,613/month but only $170,389 in total interest. The 15-year option saves you $212,244 — enough to buy a second property. The monthly difference is $717, but the lifetime savings are extraordinary. If you can afford the higher payment, the 15-year term is almost always the better financial decision.
The Power of Extra Payments
Adding just $200/month extra to a $300,000 mortgage at 6.5% for 30 years saves approximately $95,000 in interest and pays off the loan 6.5 years early. One extra full payment per year (13 payments instead of 12) saves approximately $72,000 and shortens the loan by 4.5 years. Even rounding up your payment to the next $100 makes a measurable difference over the life of the loan.