Mortgage Comparison Calculator
Compare two home loan offers or a refinance against your current loan: monthly P&I, fees, balance left and net cost over the months you expect to keep the loan.
Interactive calculator · Method MORTGAGE-COMPARISON-1.0 · Last reviewed: 2026-11-04
Calculate your scenario
Each loan’s monthly principal and interest is M = P × r ÷ (1 − (1 + r)^−n), with r = annual rate ÷ 12 ÷ 100 and n = term in months (M = P ÷ n at 0%).
Your inputs
Default worked example. Edit the inputs to calculate your scenario.
Default worked example
Over 84 months, net cost = payments + upfront costs + balance still owed: Offer A $433,529.88 vs Offer B $428,631.67, so Offer B is lower by $4,898.20.
How to use the calculator
Pick two offers or a refinance. Enter how many months you expect to keep the loan before selling or refinancing again. For offers, enter one loan amount and each offer’s rate, term and upfront fees including points. For a refinance, enter your current balance, rate and months remaining, then the new rate, term, closing costs and any cash-out.
What the result means
With a $300,000 loan kept 84 months, Offer B’s lower 6.125% rate saves $73.37 a month and recovers its extra $3,000 of fees in about 40.9 months, so it ends up $4,898.20 lower in net cost than Offer A.
Formula and units
Each loan’s monthly principal and interest is M = P × r ÷ (1 − (1 + r)^−n), with r = annual rate ÷ 12 ÷ 100 and n = term in months (M = P ÷ n at 0%). The balance after k payments is B = P(1 + r)^k − M((1 + r)^k − 1) ÷ r, where k is the horizon or the term, whichever is shorter. Net cost at the horizon = payments made + upfront fees or closing costs + balance still owed; for a refinance the cash-out received is subtracted, and the new loan is the current balance plus cash-out. Simple break-even = extra upfront cost ÷ monthly payment saving.
Worked examples
Two 30-year offers with different points, kept 84 months: Months you expect to keep the loan: 84 months; Loan amount (offers): 300000 USD; Offer A annual rate: 6.5 %; Offer A term: 30 years; Offer A upfront fees and points: 3000 USD; Offer B annual rate: 6.125 %; Offer B term: 30 years; Offer B upfront fees and points: 6000 USD; Current loan balance (refinance): 250000 USD; Current loan annual rate: 7.25 %; Current loan months remaining: 300 months; New loan annual rate: 6 %; New loan term: 30 years; Refinance closing costs paid upfront: 5000 USD; Cash-out added to the new loan: 0 USD; Comparison: offers.
Example result: Lower net cost at horizon: Offer B by $4,898.20; Monthly P&I: Offer A $1,896.20 · Offer B $1,822.83 (change -$73.37); Paid by horizon incl. fees: Offer A $162,281.14 · Offer B $159,117.86; Balance owed at horizon: Offer A $271,248.73 · Offer B $269,513.82; Net cost at horizon: Offer A $433,529.88 · Offer B $428,631.67; Simple break-even: Offer B recovers $3,000.00 extra upfront in 40.9 months.
Refinance 7.25% to 6% on a $250,000 balance over 60 months: Months you expect to keep the loan: 60 months; Loan amount (offers): 300000 USD; Offer A annual rate: 6.5 %; Offer A term: 30 years; Offer A upfront fees and points: 3000 USD; Offer B annual rate: 6.125 %; Offer B term: 30 years; Offer B upfront fees and points: 6000 USD; Current loan balance (refinance): 250000 USD; Current loan annual rate: 7.25 %; Current loan months remaining: 300 months; New loan annual rate: 6 %; New loan term: 25 years; Refinance closing costs paid upfront: 5000 USD; Cash-out added to the new loan: 0 USD; Comparison: refi.
Example result: Lower net cost at horizon: Refinance by $10,573.14; Monthly P&I: Current $1,807.02 · Refinance $1,610.75 (change -$196.26); Paid by horizon incl. fees: Current $108,421.03 · Refinance $101,645.21; Balance owed at horizon: Current $228,627.54 · Refinance $224,830.22; Net cost at horizon: Current $337,048.57 · Refinance $326,475.43; Simple break-even: Refinance recovers $5,000.00 extra upfront in 25.5 months.
Limitations and common mistakes
Rates, fees and closing costs are the figures you enter from your own quotes; nothing here is a live or advertised rate, and the defaults are only examples. Payments are unrounded fixed-rate principal and interest only, without taxes, insurance, mortgage insurance or adjustable-rate resets. Closing costs are treated as paid in cash, not rolled into the loan. Net cost ignores the time value of money, tax effects and prepayment penalties. A comparison, not a loan offer or advice.
Comparing only monthly payments. A lower payment from a longer new term or a points-heavy offer can still cost more if you sell or refinance before the break-even month.
Sources and assumptions
Method MORTGAGE-COMPARISON-1.0; last formula review 2026-11-04. Sources and their supported claims. Calculation methodology.