Mortgage Calculator
Editorial Review
We check the math, keep the copy readable, and call out what each calculator is not for — by DP Tech Studio.
Reference sources
Important: This calculator estimates principal and interest only. It does not include property taxes, homeowners insurance, PMI, or HOA fees, which can significantly affect your actual monthly payment.
What This Mortgage Calculator Shows You
A mortgage calculator helps you estimate your monthly home loan payment before you sit down with a lender. By entering your home price, down payment, interest rate, and loan term, you get an instant picture of what your principal-and-interest payment will look like — and how much interest you will pay over the life of the loan.
This is one of the most useful tools in the home-buying process because it lets you compare scenarios quickly. Want to see how a 15-year mortgage compares to a 30-year? Wonder what happens if you put 20% down instead of 10%? You can try both in seconds.
How the Mortgage Payment Formula Works
The monthly payment is calculated using the standard amortization formula for fixed-rate mortgages:
Where:
L = Loan amount (Home price − Down payment)
r = Monthly interest rate (Annual rate ÷ 12 ÷ 100)
n = Total number of payments (Years × 12)
The "P&I" label is standard industry shorthand for principal and interest — the two components your calculator handles. Other line items like taxes and insurance are handled by your escrow account separately.
Worked Example
Down Payment: $70,000 (20%)
Loan Amount: $280,000
Annual Rate: 6.5%
Loan Term: 30 years (360 months)
Monthly Rate (r): 6.5 / 12 / 100 = 0.005417
Monthly P&I Payment: ≈ $1,770
Total Payment: $1,770 × 360 = $637,200
Total Interest: $637,200 − $280,000 = $357,200
Down Payment: How Much Is Enough?
The conventional wisdom is 20%, but it is not a hard rule. Here is what different down payment levels mean in practice:
- Less than 20%: Most lenders require private mortgage insurance (PMI), typically 0.5–1.5% of the loan amount annually. This adds to your monthly cost until you reach 20% equity.
- 20%: The standard threshold. You avoid PMI, get better rate offers from most lenders, and start with meaningful equity.
- More than 20%: A larger down payment reduces your loan balance, lowers your monthly payment, and often earns a marginally better interest rate. It also reduces lifetime interest paid.
15-Year vs. 30-Year Mortgage
This is one of the most common trade-off questions in home buying. Here is a direct comparison using the $280,000 example above:
- 30-year at 6.5%: ~$1,770/month, ~$357,000 total interest paid
- 15-year at 6.0% (rates are typically lower on shorter terms): ~$2,363/month, ~$145,000 total interest paid
The 15-year mortgage costs about $600 more per month but saves over $200,000 in interest and builds equity much faster. Whether that is the right choice depends entirely on your cash flow, emergency fund, and other financial goals. Run both scenarios in this calculator before deciding.
What This Calculator Does Not Include
Your actual monthly housing cost will almost always be higher than the P&I figure shown here. Make sure to factor in:
- Property taxes — typically 1–2% of home value annually, collected monthly via escrow
- Homeowners insurance — required by all lenders, usually $100–$200/month for most homes
- PMI — required if your down payment is below 20%, adds $100–$400/month on many loans
- HOA fees — common in condos and planned communities, ranges from $100 to $1,000+/month
- Maintenance costs — financial planners often suggest budgeting 1% of home value per year
Common Mistakes to Avoid
These are the errors that come up most often when people use a mortgage calculator for the first time:
- Using the monthly payment as your total housing cost — The P&I figure is only part of what you'll actually pay each month. Property tax, homeowners insurance, and PMI (if applicable) can easily add $400–$800 more, depending on your location and loan size. Always add these before comparing with your budget.
- Entering the full home price instead of the loan amount — The calculator uses Home Price minus Down Payment to get the loan amount. If you enter the full price in the wrong field, your result will be significantly overstated.
- Using a rate you saw online without checking your own eligibility — Advertised mortgage rates typically assume a 760+ credit score and 20% down. If your credit score is 680 or your down payment is 10%, your actual rate offer from a lender will likely be higher.
- Forgetting that a lower monthly payment isn't always cheaper — A 30-year loan has a lower monthly payment than a 15-year loan, but you pay more than double the interest over the loan's life. Run both scenarios before deciding which term fits your actual financial goals.
- Comparing APR and interest rate interchangeably — The interest rate determines your monthly P&I payment. The APR includes fees and closing costs spread over the loan life and is a better number for comparing lenders. This calculator uses the interest rate, not APR.