How to Use
Enter the amount you plan to borrow (not the full purchase price).
Optionally add a down payment to reduce the financed principal.
Input the annual interest rate as a percentage (e.g. 6.5 for 6.5%).
Set the loan term in years, such as 15 or 30.
Click Calculate to generate your payment breakdown and amortization table.
How the Amortization Formula Works
The formula M = P x [r(1+r)^n] / [(1+r)^n − 1] drives every fixed rate mortgage. P is the principal (loan amount minus down payment), r is the monthly rate (annual rate divided by 12 divided by 100), and n is total payments (years times 12). Each month, interest equals the current balance times r. The rest of the fixed payment chips away at principal. Because the balance shrinks with every payment, the interest portion decreases over time and the principal portion grows until the loan reaches zero.
Worked Example
- Loan amount: 300,000 with no down payment, so P = 300,000.
- Annual rate 6.5% gives a monthly rate r = 6.5 / 12 / 100 = 0.005417.
- A 30 year term means n = 360 monthly payments.
- Plugging into the formula: M = 300,000 x (0.005417 x 1.005417^360) / (1.005417^360 − 1) = roughly 1,896.
- Over 360 payments the total cost is about 682,600, meaning roughly 382,600 goes to interest alone.
When This Calculator Helps
- Before applying for a mortgage, to know what monthly payment to expect.
- Comparing 15 year vs. 30 year terms to weigh payment size against lifetime interest.
- Testing how a larger down payment reduces both monthly cost and total interest.
- Estimating how much house you can afford based on a target monthly budget.
- Running refinance scenarios with a remaining balance and a new rate.
- Preparing numbers for a conversation with a mortgage broker or financial planner.
Keep in Mind
These results are mathematical estimates only. They exclude property taxes, homeowner's insurance, PMI, HOA dues, and any lender fees. Rates change daily and your actual rate depends on credit profile and market conditions. Confirm all figures with a licensed mortgage professional before committing.
Getting the Most from This Calculator
Key Features
Instant Payment Calculation
Computes your exact monthly payment from the standard amortization formula using principal, rate, and term.
Full Amortization Table
Shows the first 12 months in detail plus a yearly summary of how principal, interest, and remaining balance shift over the loan.
Yearly Chart
A stacked bar chart breaks down principal versus interest paid each year so you can see the crossover point at a glance.
PDF Export
Download a formatted PDF of your results to share with a broker or keep for your records.
Private by Design
All math runs locally in JavaScript. No loan data, rates, or personal information ever leave your browser.
Privacy
All mortgage calculations run entirely in your browser using JavaScript. No loan amounts, rates, or personal data are transmitted to any server.
Frequently Asked Questions
What is an amortization schedule?
It breaks each payment into its principal and interest portions alongside the remaining balance. Early in the loan most of each payment covers interest; later payments shift heavily toward principal reduction.
Does this include taxes and insurance?
No. The calculator covers principal and interest only. Your actual monthly housing cost will also include property taxes, homeowner's insurance, and possibly private mortgage insurance.
Can I use this for refinancing?
Enter your remaining balance as the loan amount, the new interest rate, and the new term length. The output lets you compare the refinanced payment against your current one.
Why is total interest so high on a 30 year mortgage?
Interest compounds on a large balance over many years. At 7% for 30 years, total payments roughly double the original principal. Shorter terms cut total interest substantially but raise the monthly payment.