EXAMPLE inputs — $400,000 price, 20% down, 6.5% annual, 30 years. Not a current market rate.
EXAMPLE loaded. Calculate to see principal and interest.
Monthly principal + interest
—Total paid
—Total interest
—Months saved with extra payment
—The formula
M = P × r(1+r)n / ((1+r)n − 1)
M is the monthly principal-and-interest payment. P is the loan principal (home price minus down payment). r is the monthly rate: annual interest rate divided by 12, then divided by 100. n is the number of monthly payments: term in years times 12.
If the annual rate is 0%, there is no interest, so M is simply P divided by n.
EXAMPLE: a $400,000 price with $80,000 down leaves $320,000 of principal. At 6.5% annual for 30 years, r is 6.5 ÷ 12 ÷ 100 and n is 360. That scheduled payment is about $2,022 a month of principal and interest.
How to calculate it
- Subtract the down payment from the home price to get principal P.
- Convert the annual rate to a monthly decimal r (divide by 12, then by 100).
- Multiply years by 12 to get n, the payment count.
- Plug P, r, and n into the formula for M. That is principal and interest only.
Educational estimate of principal and interest only. Does not include property taxes, homeowners insurance, HOA dues, or PMI. Not financial advice. Defaults are labeled EXAMPLE and are not a quoted market rate.
FAQ
What formula is used to calculate mortgage payments?
The standard amortization formula is M = P × r(1+r)^n / ((1+r)^n − 1). P is principal, r is the monthly rate (annual rate divided by 12 then by 100), and n is the number of months (years × 12). If the rate is 0%, M is P divided by n.
What is not included in this monthly payment?
This is principal and interest only. It does not include property taxes, homeowners insurance, HOA dues, or PMI. Those extra costs are often escrowed with a real mortgage payment.
Is mortgage interest compounded monthly in this calculator?
Yes. The annual rate is converted to a monthly rate and applied once per month, which is the usual fixed-rate amortization schedule. It is not daily compounding and not a quoted APR with fees.
How does an extra monthly payment shorten the loan?
Any extra amount above the scheduled principal-and-interest payment goes to principal. That lowers the balance faster, so fewer months of interest accrue. This page reports months saved versus the original term.
Do I need an account or upload anything?
No. The calculator runs in your browser with JavaScript. Nothing is uploaded and there is no account.