This mortgage calculator estimates monthly principal and interest from the property price, down payment, loan rate, and term. Optional tax, insurance, and other monthly costs provide a broader housing-payment estimate.
How to use this calculator
Enter the purchase price and down payment; the financed amount is the difference. Add the fixed annual rate and term. Optional annual tax and insurance are divided by twelve and added to other monthly costs.
Formula & calculation method
Monthly principal and interest = L × i / (1 − (1 + i)^−N)The financed principal L is price minus down payment. The monthly rate i is the annual nominal rate divided by twelve, and N is years multiplied by twelve. Total interest is the sum of principal-and-interest payments minus the original financed amount.
Worked example
For a 350,000 property with 70,000 down, the model finances 280,000. At a fixed rate over 30 years, it reports the core loan payment, total interest, and an optional total monthly housing figure when additional costs are entered.
Why this is useful
Separating loan cost from optional housing expenses makes the estimate easier to interpret. You can compare down payments or terms and see both monthly affordability and long-term interest implications.
Limitations to keep in mind
The model excludes lender fees, mortgage insurance that varies by balance, association dues unless entered manually, escrow changes, and rate adjustments. Taxes and insurance can change, so the total housing payment is only an estimate.
Frequently asked questions
Does a larger down payment always reduce interest?
With the same rate and term, it reduces the financed principal, which normally lowers both the monthly payment and total interest.
Are taxes and insurance fixed?
No. The calculator divides your current annual estimates by twelve, but real charges may change over time.
Can the down payment equal the price?
Yes. In that case no loan payment or interest is calculated, and only any optional monthly costs remain.