How our calculators work
Every number on this site is produced by standard, documented financial mathematics — no proprietary black boxes. Here is exactly what runs under the hood.
The core formulas
Our calculators use the same time-value-of-money functions built into spreadsheets and used by lenders:
- Payment (PMT). The fixed periodic payment that amortizes a loan:
Payment = P · r ÷ (1 − (1 + r)⁻ⁿ), wherePis the principal,rthe periodic interest rate (annual ÷ 12), andnthe number of payments. - Amortization. Each period we charge interest on the outstanding balance (
balance · r), apply the rest of the payment to principal, and carry the new balance forward — producing the full schedule. - Present & future value (PV / FV). Used for affordability, required-income and savings-style tools to solve for a loan amount or balance.
- Effective APR. Where fees or points are involved, we solve for the rate that equates the financed amount to the present value of the payments.
Assumptions we make
Unless a calculator asks for it, results assume a fixed interest rate, equal monthly payments, interest compounded monthly, and that extra payments are applied directly to principal. Property tax, insurance, PMI and HOA dues are included only where the tool provides fields for them. Adjustable-rate tools project future rates using the inputs you provide and cannot predict actual index movements.
How we test the calculators
Every time the site is built, the scenarios below are re-run. The expected value comes from an independent reference — a published textbook figure, or the closed-form payment formula and a separate month-by-month payoff loop written apart from our engine. The engine value is what the calculators on this site return. Each check has its own tolerance: a cent for monthly payments and rates, and up to a dollar where the engine rounds to whole dollars (lifetime interest, equity and cash-out projections). If any pair falls outside its tolerance, the build stops and nothing is published.
| Scenario | Expected | Our engine | Result |
|---|---|---|---|
| Textbook payment $200,000 at 6.00% for 30 years — the standard published example | $1,199.10 | $1,199.10 | Pass |
| Today’s default loan $340,000 at 7.18% for 30 years (the calculator’s starting inputs) | $2,303.28 | $2,303.28 | Pass |
| 15-year term $500,000 at 5.50% for 15 years | $4,085.42 | $4,085.42 | Pass |
| Zero-interest edge case $300,000 at 0% for 30 years — must not divide by zero | $833.33 | $833.33 | Pass |
| Schedule closes at $0 Final balance after the last of 360 payments | $0.00 | $0.00 | Pass |
| Principal repaid = amount borrowed Sum of every principal payment in the schedule | $340,000.00 | $340,000.00 | Pass |
| Extra $200 a month — payoff time $300,000 at 6.50%, 30 years, $200 extra principal monthly | 277 months | 277 months | Pass |
| Extra $200 a month — total interest Same loan: lifetime interest with the extra payments | $279,184.67 | $279,184.67 | Pass |
| PMI at 3% down $350,000 home, $10,500 down: 0.7% a year on the $339,500 loan | $198.04 | $198.04 | Pass |
| Zero down payment (100% LTV) $400,000 home, $0 down: PMI on the full balance | $233.33 | $233.33 | Pass |
| PMI at 5% down $400,000 home, $20,000 down: 0.7% a year on the $380,000 loan | $221.67 | $221.67 | Pass |
| PMI at 10% down $400,000 home, $40,000 down: 0.7% a year on the $360,000 loan | $210.00 | $210.00 | Pass |
| PMI at 19.9% down $400,000 home, $79,600 down: 0.7% a year on the $320,400 loan | $186.90 | $186.90 | Pass |
| No PMI at exactly 20% down $425,000 home, $85,000 down (80% loan-to-value) | $0.00 | $0.00 | Pass |
| Full monthly payment (PITI) Default inputs: P&I + 1% property tax + $2,000/yr insurance | $2,824.11 | $2,824.11 | Pass |
| Refinance — new payment $300,000 refinanced at 6.50% for 30 years | $1,896.20 | $1,896.20 | Pass |
| Refinance — same rate and term, no costs $300,000 at 7.00%, 25 years left → 7.00% for 25 years, $0 costs: net after 5 years must be $0 | $0.00 | $0.00 | Pass |
| Refinance — costs only Same loan with $5,000 closing costs: net after 5 years must be −$5,000 | $-5,000.00 | $-5,000.00 | Pass |
| Refinance — stretched term counts what you still owe $300,000 at 7.50% with 22 years left → 6.50% for 30 years, $6,000 costs: net after 5 years (paid + owed) | $6,276.03 | $6,276.03 | Pass |
| Should I refinance — stretched term $300,000 at 7.50% with 20 years left → 7.40% for 30 years, $7,000 costs, staying 7 years: the payment drops but you end up behind, so the verdict must be "No" | No | No | Pass |
| Home equity — amount you could borrow $450,000 home, $260,000 mortgage + $15,000 HELOC, 85% CLTV limit: 450,000 × 0.85 − 275,000 | $107,500.00 | $107,500.00 | Pass |
| Home equity — equity in 5 years Same home at 0% price change, $260,000 at 6.00% with 25 years left: value − balance after 60 payments − $15,000 | $201,176.57 | $201,177.00 | Pass |
| 40-year mortgage — monthly payment $400,000 at 7.25% over 480 months (closed-form payment formula) | $2,558.69 | $2,558.69 | Pass |
| 40-year mortgage — balance after 10 years Same loan after 120 payments, from a separate month-by-month loop | $375,077.20 | $375,077.00 | Pass |
| Cash-out — most cash in hand $450,000 home, $250,000 owed, 80% cap, 3% costs taken from the cash: 360,000 − 250,000 − 3% × 360,000 | $99,200.00 | $99,200.00 | Pass |
| Cash-out — cash in hand Same home, $50,000 cash out: 50,000 − 3% × 300,000 new loan | $41,000.00 | $41,000.00 | Pass |
| Cash-out — vs. keeping the loan + a second, 10 years Paid + still owed after 10 years: keep + second − cash-out (negative = the refinance costs more) | $-87,066.52 | $-87,066.52 | Pass |
| VA cash-out — most cash with the funding fee inside 100% $450,000 home, $250,000 owed, 2.15% fee financed inside the cap, 3% costs from the cash: 450,000 ÷ 1.0215 × 0.97 − 250,000 | $177,312.78 | $177,313.00 | Pass |
| FHA cash-out — upfront MIP added on top $300,000 base loan (80% limit not counting the premium) × 1.0175 | $305,250.00 | $305,250.00 | Pass |
| FHA cash-out — annual MIP over 11 years 0.50% a year, paid monthly on the falling balance of $305,250 at 7.13%, 132 months | $15,633.18 | $15,633.18 | Pass |
| Down payment help — cash to close $350,000 home: 3.5% down + 3% closing costs = $22,750, minus $10,000 of assistance | $12,750.00 | $12,750.00 | Pass |
| Repayable second — what the help is worth after 5 years $10,000 at 7% over 10 years: +10,000 − 60 payments − balance still owed (= minus the interest paid) | $-2,830.22 | $-2,830.22 | Pass |
| Grant with a higher program rate — net value after 7 years $10,000 grant; $337,750 first mortgage at 6.875% instead of 6.50%: 10,000 − 84 months of extra payments − the higher balance | $1,080.34 | $1,080.34 | Pass |
| State programs — cash still needed $400,000 home: 3.5% down ($14,000) + $4,000 closing costs, minus $10,000 of assistance | $8,000.00 | $8,000.00 | Pass |
| State programs — help capped at the cash needed Same home with $50,000 of assistance: covers the $18,000 needed, never cash back | $0.00 | $0.00 | Pass |
| State programs — income to afford the home $386,000 loan at 6.50%: P&I + 0.55% FHA premium + 1% tax + 0.5% insurance, × 12 ÷ 28% | $133,572.82 | $133,572.82 | Pass |
| MCC — loan larger than the certified amount Pub. 530: $125,000 loan, $100,000 certified, $7,500 interest → $6,000 counts; × 20% | $1,200.00 | $1,200.00 | Pass |
| MCC — 20% rate is not capped $13,500 of interest × 20% (the $2,000 cap applies only above 20%) | $2,700.00 | $2,700.00 | Pass |
| MCC — 40% rate capped at $2,000 $13,500 × 40% = $5,400, limited to $2,000 by 26 U.S.C. §25(a)(2) | $2,000.00 | $2,000.00 | Pass |
| MCC — credit above your tax carries forward Pub. 530: $1,700 credit, $1,100 tax → $600 carried to later years | $600.00 | $600.00 | Pass |
| MCC — year-1 credit from the payment schedule $300,000 at 6.50% for 30 years: 12 payments minus principal repaid = year-1 interest; × 20% | $3,880.25 | $3,880.25 | Pass |
| MCC recapture — sale in year 4 $200,000 loan: 6.25% × 80% holding × income % ((94,000 − 80,000·1.05³) ÷ 5,000, rounded) vs half the $30,000 gain | $2,800.00 | $2,800.00 | Pass |
| Affordability — income needed for a home $410,700 home, 20% down, 30 years at 7.32%: P&I × 12 ÷ 28% | $96,727.68 | $96,727.68 | Pass |
| Affordability — what an $80,000 salary buys Highest price whose P&I + 0.91% tax + 0.40% insurance is 28% of $80,000 a year (round trip) | $80,000.00 | $80,000.00 | Pass |
| Affordability — price and rate effects add up 2019 ($306,000 at 3.94%) to now ($410,700 at 7.32%): price effect + rate effect = total change | $47,002.22 | $47,002.22 | Pass |
45 of 45 scenarios passed — last run November 7, 2026.
Where our data comes from
Market figures are pulled by script from the primary publisher, shown with their own date, and linked to the source. Rate tables refresh weekly; anything older than three weeks is hidden rather than shown as current.
An average is not your offer. Freddie Mac's survey describes conventional, conforming, fully amortizing loans for borrowers who put 20% down and have excellent credit; Optimal Blue's indices describe rates lenders actually locked that day for each program. Your own rate depends on your credit score, down payment, points and lender. Where no series measures a loan directly, we show a labelled benchmark (a related average the loan usually prices above), an adjustable-rate loan's starting rate, or the index a loan floats on — or say that no published average exists.
| Data | Source | Source publishes |
|---|---|---|
| 30- and 15-year fixed rates | Freddie Mac Primary Mortgage Market Survey (PMMS), via FRED | Weekly (Thursdays) |
| FHA, VA, USDA, jumbo and conforming rates | Optimal Blue Mortgage Market Indices (OBMMI), via FRED | Daily |
| 20-year, 10-year and 5/1 ARM rates | Zillow national averages, as published by NerdWallet — entered by hand | Daily; hidden on our site once older than 21 days |
| Prime rate (HELOC index) | Bank prime loan rate, via FRED | Daily |
| Median listing prices | Realtor.com housing inventory data, via FRED | Monthly |
| Applications, approval and denial rates, lender volumes and pricing | Home Mortgage Disclosure Act (HMDA) data, FFIEC / CFPB | Annually |
| Mortgage complaints | CFPB Consumer Complaint Database | Daily |
| Property tax and insurance by state | U.S. Census Bureau, American Community Survey microdata (PUMS) | Annually |
| Conforming loan limits | Federal Housing Finance Agency (FHFA) | Annually |
| Price adjustments by credit score and LTV | Fannie Mae Loan-Level Price Adjustment Matrix — compared with the live PDF by script | When Fannie Mae updates it (several times a year) |
How we compare what lenders' borrowers paid
The "rates and costs" figures on our lender reviews and state lender pages come from 2025 HMDA loan-level records published by the FFIEC and CFPB — 3,576,617 home-purchase loans originated nationwide, downloaded state by state and checked against HMDA's own counts. They show what borrowers actually got, not advertised rates.
- Like-for-like loans only. First-lien, owner-occupied, single-family site-built homes, 30-year fixed rate, with no interest-only, balloon or negative-amortization features. Conventional and jumbo loans are limited to 20% or more down, so private mortgage insurance doesn't distort the comparison; FHA and VA loans are compared with other FHA and VA loans.
- APR vs benchmark is the median rate spread: the loan's APR minus the average prime offer rate (APOR) for a comparable loan in the week the rate was set. Because the benchmark moves with the market, it compares lenders no matter when in the year they lent. A negative number means borrowers paid less than the benchmark.
- Loan costs are the borrower-paid "total loan costs" from the Closing Disclosure — origination charges plus required and shopped-for services. For FHA loans they include the 1.75% upfront mortgage insurance premium; for VA loans, the funding fee where it applies (veterans with a service-connected disability are exempt, which lowers some lenders' medians). They exclude taxes, prepaid interest, escrow deposits and the down payment.
- Discount points are counted whoever paid them — buyer, seller or builder. Points the buyer pays are already reflected in the APR; points a seller or builder pays lower the APR without costing the buyer, which is why homebuilder-owned lenders can show far-below-market figures.
- Minimums. A lender's medians are published for a loan type only with at least 100 comparable loans nationally, and 30 within a state.
The limits matter: the public data has no credit scores, and relationship discounts, points and seller credits vary by borrower. These medians tell you whether a quote is in the normal range for a lender — they are not the rate you will be offered. We refresh them once a year, when HMDA publishes a new year of data.
What the results are — and aren't
Results are precise mathematical estimates, not quotes or approvals. Your actual loan terms depend on your lender, credit profile, local taxes and program rules that no general calculator can fully capture. We round displayed figures for readability while computing at full precision.
Keeping it current
Default rates refresh every week from Freddie Mac and Optimal Blue; loan limits, FHA and VA fees and tax thresholds are reviewed when the agencies publish new figures (usually once a year). Where a figure is time-sensitive (such as a loan limit or a typical rate), treat it as a starting point and confirm the current number with your lender.
Found an error?
We take accuracy seriously. If a result looks wrong, please tell us — we investigate every report and correct genuine errors promptly.