Principal, interest and extra payments
For a fixed-rate loan, monthly principal and interest = L × r ÷ [1 − (1 + r)−n], where L is principal, r is the annual percentage rate divided by 1,200, and n is the number of payments. At a zero rate, payment = L ÷ n. Each month’s interest is the opening balance multiplied by r; principal reduces the balance. Actual lender rounding and payment dates can differ.
Mortgage insurance and upfront fees
Conventional PMI is an illustrative credit-score/LTV estimate, not an insurer quote. Automatic termination is modeled using the original amortization schedule at 78% of original value, with a midpoint backstop. Earlier cancellation at 80% may be requested subject to requirements; extra payments do not automatically cancel PMI.
FHA annual MIP is estimated from scheduled annual average balances using HUD’s premium calculation procedure and applicable duration. Financed upfront MIP is excluded from the annual premium basis through the HUD adjustment. USDA annual fees use scheduled annual average note balances. Fully financed USDA upfront fees are calculated on the total loan including the fee. VA funding fees depend on down payment, prior use and exemption. This model does not determine eligibility, loan limits or case-specific exceptions.
Official references
- HUD mortgage insurance premium calculations
- CFPB: PMI cancellation and automatic termination
- USDA guarantee fees, Chapter 16
- VA funding fees
Rates, comparisons and omissions
National average mortgage rates are informational averages; the displayed retrieval date is not a guarantee that rates changed on that date. Shared scenarios retain the rate entered. APR, variable rates, discount-point break-even, penalties, tax deductions, eligibility and lender-specific pricing are not modeled. Refinance results compare fixed-rate schedules and entered closing costs. Biweekly is an approximation of one extra yearly payment spread monthly.
Updated September 18, 2026.
Principal, interest and extra payments
For a fixed-rate loan, monthly principal and interest = L × r ÷ [1 − (1 + r)−n], where L is principal, r is the annual percentage rate divided by 1,200, and n is the number of payments. At a zero rate, payment = L ÷ n. Each month’s interest is the opening balance multiplied by r; principal reduces the balance. Actual lender rounding and payment dates can differ.
Mortgage insurance and upfront fees
Conventional PMI is an illustrative credit-score/LTV estimate, not an insurer quote. Automatic termination is modeled using the original amortization schedule at 78% of original value, with a midpoint backstop. Earlier cancellation at 80% may be requested subject to requirements; extra payments do not automatically cancel PMI.
FHA annual MIP is estimated from scheduled annual average balances using HUD’s premium calculation procedure and applicable duration. Financed upfront MIP is excluded from the annual premium basis through the HUD adjustment. USDA annual fees use scheduled annual average note balances. Fully financed USDA upfront fees are calculated on the total loan including the fee. VA funding fees depend on down payment, prior use and exemption. This model does not determine eligibility, loan limits or case-specific exceptions.
Official references
- HUD mortgage insurance premium calculations
- CFPB: PMI cancellation and automatic termination
- USDA guarantee fees, Chapter 16
- VA funding fees
Rates, comparisons and omissions
National average mortgage rates are informational averages; the displayed retrieval date is not a guarantee that rates changed on that date. Shared scenarios retain the rate entered. APR, variable rates, discount-point break-even, penalties, tax deductions, eligibility and lender-specific pricing are not modeled. Refinance results compare fixed-rate schedules and entered closing costs. Biweekly is an approximation of one extra yearly payment spread monthly.
Updated September 18, 2026.