Put two mortgage options side by side — different rates, terms, or loan amounts — and see the real cost difference over the life of each loan.
Two quotes land in your inbox, $14 a month apart, and the easy move is to shrug and take whichever loan officer called you back first. That $14 a month is a $52,000 lie. Over 30 years the cheaper-feeling payment can quietly cost you a luxury car's worth of extra interest — because the payment is what you feel every month and the total interest is what the loan actually costs you. This calculator puts both numbers side by side. You enter Loan Amount, Interest Rate, and Term for each of two options, and it returns the monthly payment, total interest paid, and total cost of ownership for each, plus the gap between them.
The comparison is most useful when you are evaluating competing lender quotes, weighing a rate buydown, or deciding between a 15-year and a 30-year term. Two loans that look similar on monthly payment can have dramatically different total cost pictures, and vice versa. Seeing both columns side by side makes the real trade-off visible.
Monthly payment versus total interest: why both numbers matter
The monthly payment determines whether you can afford the house and make the payment every month. Total interest paid determines the actual cost of the money you borrowed over the full loan term. These two metrics optimize against each other: the strategy that minimizes monthly payment (longer term, lower monthly obligation) tends to maximize total interest paid. The strategy that minimizes total interest (shorter term, higher monthly obligation) requires a payment that may strain current cash flow.
The calculator puts both numbers on the table simultaneously for each loan option so you can make the trade-off explicitly. A 15-year loan at 6.75% on a $350,000 balance carries a monthly payment of roughly $3,090 and total interest of about $207,000. The same loan at 30 years at 7.25% carries $2,390/month and total interest of $510,000. The 30-year option saves $700/month; the 15-year option saves $303,000 in interest. That is the decision.
Rate buydowns: what a lower rate actually costs and saves
A rate buydown — paying discount points at closing to secure a lower interest rate — is a classic use case for this calculator. Loan A might reflect a market-rate offer at 7.25% with no points; Loan B might be the same loan bought down to 6.75% with 2 points ($7,000 on a $350,000 loan). The calculator shows you the monthly payment difference and total interest difference, so you can compute the break-even period: how many months of lower payments cover the upfront buydown cost.
At 7.25% on $350,000 for 30 years, monthly P&I is roughly $2,388. At 6.75%, it drops to about $2,270. Monthly savings: $118. Upfront cost to buy down: $7,000. Break-even: $7,000 / $118 = about 59 months — just under 5 years. If you plan to stay in the home and keep the loan longer than 5 years, the buydown saves money. If you plan to sell or refinance before then, it does not. The calculator gives you the payment and interest numbers to run that calculation.
Comparing lender quotes for the same loan type
When shopping lenders, a seemingly small rate difference can add up significantly. Two lenders offering the same loan amount and term at 7.125% versus 7.375% appear nearly identical at first glance — a 0.25% difference. On a $400,000 loan over 30 years, the lower rate saves about $68/month in payment and roughly $24,500 in total interest. That is a number worth knowing before you commit to a lender.
The comparison also works for lenders offering different loan structures on the same purchase: a credit union offering a 30-year at 6.99% with $2,000 in lender fees versus a bank offering 6.875% with $5,500 in origination fees. The calculator handles the loan amounts and rate differences; you would need to separately factor in the fee difference. Load Loan A with the lower-fee lender's rate and Loan B with the lower-rate lender's rate, then compare total interest paid against the fee differential.
ARM versus fixed: modeling the risk over the initial fixed period
Adjustable-rate mortgages start at a lower rate for an initial fixed period — typically 5, 7, or 10 years — before adjusting annually based on a benchmark index. The calculator is most useful for comparing an ARM against a fixed loan over the initial fixed period, using the ARM's starting rate and the fixed loan's rate side by side. This shows the monthly payment advantage of the ARM and the total interest savings over the initial period.
What the calculator cannot model is the adjustment risk after the fixed period ends. An ARM that starts at 6.25% for 7 years against a 30-year fixed at 7.0% looks attractive on a 7-year horizon. But if rates rise and the ARM adjusts to 9% at year eight, the 30-year fixed buyer was protected while the ARM borrower faces a much higher payment. Use the comparison to understand the initial-period advantage of an ARM; the rate adjustment risk is a separate analysis beyond the scope of any simple comparison tool.
The refinance trap: a lower payment that quietly costs more
Refinancing replaces an existing mortgage with a new one — and the economics depend entirely on the comparison between keeping the current loan and taking the new one. Loan A in this scenario is your current remaining balance, current rate, and remaining term. Loan B is the proposed refinance amount, new rate, and new term (which may reset to 30 years even if only 20 remain on the current loan).
The You Save output — the difference in total cost between the two loans — tells you the gross benefit of the refinance before closing costs. If Loan A costs $287,000 in remaining interest and Loan B costs $235,000, the gross savings is $52,000. Divide that by the estimated closing costs of the refinance to see how many years of staying in the home pays off the closing cost investment. This is a more complete picture than comparing monthly payments alone and prevents the common mistake of refinancing into a lower payment that costs more in total over the new extended term.
How to use it
- Enter Loan Amount for Loan A — the principal balance for the first option.
- Set Interest Rate % and Term (years) for Loan A.
- Enter the same fields for Loan B — the second mortgage option you are comparing.
- Read Monthly Payment, Total Interest, and Total Cost for each loan side by side.
- Use the You Save output and Rate Difference to quantify which option costs less over the full term.
Who it's for
- Buyer comparing two lender quotes on the same purchase — A buyer with quotes at 7.25% from a bank and 6.875% from a credit union for a $390,000 loan enters both rates and sees the total interest difference is $28,400 over 30 years — and decides the lower rate is worth the credit union's slightly more complex application process.
- Homeowner evaluating a refinance — An owner with $280,000 remaining at 7.5% for 26 more years compares keeping the current loan against refinancing to $280,000 at 6.5% for 30 years — sees the monthly savings and total interest cost increase from resetting the term, and decides to go 15-year instead.
- Buyer deciding on a rate buydown — A borrower compares a 7.25% no-points loan against a 6.75% loan with 2 points on a $340,000 purchase — calculates break-even at about 57 months and decides to buy down since they plan to stay long-term.
- Investor comparing a 15-year versus 30-year rental mortgage — A landlord models a 15-year at 6.5% versus a 30-year at 7.0% on a $250,000 rental — sees the 15-year costs $850/month more but saves $158,000 in total interest and uses the cash flow difference to decide which structure supports the rental's monthly expenses.
Key terms
- Amortization
- The process of paying off a loan through scheduled principal and interest payments over a defined term. Each payment reduces the principal balance while the interest component decreases and the principal component increases over time.
- Discount points
- Upfront fees paid to a lender to reduce the interest rate on a mortgage. One point equals 1% of the loan amount. Used in rate buydown scenarios to trade a higher closing cost for a lower long-term rate.
- Total interest paid
- The cumulative interest cost over the full loan term assuming no prepayments. The key metric for evaluating the long-term cost difference between two loan options.
- Break-even period
- In a rate buydown or refinance context, the number of months of lower payments required to recover an upfront cost. Calculated by dividing upfront cost by monthly payment savings.
Frequently asked questions
Does this calculator include property taxes and insurance?
No — the comparison is principal and interest only. To include PITI, use the Home Affordability Calculator or House Affordability Calculator, which build property taxes and insurance into the monthly payment estimate. The Mortgage Comparison Calculator is designed for loan-to-loan comparison on P&I specifically, which is the cleanest basis for comparing lender quotes or rate/term options.
Can I use this for a HELOC or second mortgage?
Yes — enter the HELOC or second mortgage amount as Loan A and any alternative (cash-out refi, first mortgage payoff) as Loan B. The calculator handles any fixed-rate amortizing loan. HELOCs with variable rates cannot be compared directly, but you can model the starting rate of the HELOC against a fixed alternative to understand the initial-period economics.
What does Total Cost mean in this calculator?
Total Cost is Loan Amount plus Total Interest — the full amount paid to retire the debt over the life of the loan assuming no prepayments. It does not include property taxes, insurance, PMI, or closing costs. It is the cleanest basis for comparing the cost of the money borrowed under different rate and term scenarios.
Why would I compare two loans with different loan amounts?
Common scenarios: comparing a larger loan at a lower rate versus a smaller loan after a larger down payment; comparing a conforming loan amount against a jumbo loan with different rate pricing; or comparing a full purchase price loan against a loan that incorporates a renovation budget. The calculator handles any combination of loan amount, rate, and term on each side.
How accurate is the You Save calculation?
The You Save figure is the difference in Total Cost between the two loans assuming the full term is held to maturity with no prepayments. It is accurate for comparing long-term cost of ownership but will overstate savings if either loan is likely to be refinanced or paid off early. For short hold periods, focus on monthly payment difference and adjust the savings estimate proportionally. Enter both quotes now and see the total interest difference in 30 seconds — free, no account needed.