Not financial advice
The Math Says is a planning tool. Nothing on this site is financial, tax, legal, or insurance advice. The calculators are mathematical models that use the inputs you provide; their output is a directional estimate, not a guarantee.
Your actual outcome depends on:
- Terms quoted by your lender, insurer, or advisor
- Your specific tax situation, filing status, and state
- Market conditions at the time you act
- Life events no calculator can anticipate
Verify every calculator output with a licensed professional before signing anything.
Affiliate disclosure (FTC compliance)
Some links on this site are affiliate links. If you submit a quote request, sign up for a service, or complete a transaction through one of our partners, we may earn a referral fee at no additional cost to you.
We do not let affiliate relationships dictate which calculation outputs you see. The math doesn't know about the affiliates — the math is the math. When the calculator says "don't refinance" or "skip this product," that verdict shows up exactly as the math produces it, even if a different verdict would benefit our partners.
Per the FTC's 2023 Endorsement Guidelines update, affiliate disclosure must be clear, conspicuous, and present at the point of the affiliate link. Every page footer carries this disclosure; pages with mid-content affiliate CTAs carry an additional inline note.
Mortgage planning tool
For all mortgage-related calculators on this site:
- Mortgage rates, closing costs, and fees vary by lender, state, credit profile, and market conditions at the time of application.
- Your Loan Estimate — which lenders are required to provide within 3 business days of your application under federal regulation (TRID, 2015) — is the official figure. Use our calculator to decide whether to apply; use your Loan Estimate to decide whether to sign.
- Rate quotes are typically good for 10 business days. Lock when you're committed, not before.
PMI / MIP rules
Conventional PMI rules under the Homeowners Protection Act of 1998 (12 USC §4901-4910):
- Automatic termination at 78% LTV based on original purchase price and amortization schedule
- Customer-requested cancellation available at 80% LTV (servicer may require current appraisal)
- Final termination at midpoint of amortization, whichever comes first
FHA MIP rules are different and have changed multiple times. For FHA loans originated after June 3, 2013 with less than 10% down at origination, MIP lasts the life of the loan — refinance to conventional is the only way out. For 10%+ down, MIP drops off after 11 years.
Rules are subject to change. Verify your specific situation with your servicer or HUD before refinancing solely to drop mortgage insurance.
Insurance planning tool
For the deductible optimizer and other insurance-related calculations:
- Insurance premiums, discounts, and deductible options vary by carrier, state, ZIP code, credit-based insurance score (where allowed), and your individual risk profile.
- Your binding policy declarations from your carrier override any estimate produced here.
- State law in CA, HI, MD, MA, and MI restricts how credit-based insurance scores may be used in pricing — this calculator does not model those state-specific rules.
- Past claim frequency is the best available predictor of future claims, but it's not a guarantee. Single high-cost events (catastrophic weather, fire) can dominate the math regardless of historical frequency.
Investment-comparison tools
For the pay-off-mortgage-vs-invest calculator and similar:
- Investment return assumptions in this calculator are user-supplied. We suggest defaults based on historical averages but cannot guarantee future returns.
- Past performance is not a predictor of future results. Markets can and do decline. Investment outcomes include the possibility of permanent loss.
- Mortgage interest tax deductibility depends on (a) itemizing rather than taking the standard deduction, and (b) total itemized deductions exceeding the standard deduction. Since the Tax Cuts and Jobs Act of 2017 raised the standard deduction substantially, most US households no longer deduct mortgage interest.
- Tax outcomes depend on your specific income, filing status, state, and the tax law in effect when you act.
- Consult a fiduciary financial advisor for investment-strategy decisions and a CPA for tax-implication decisions.
Auto loan and lease tool
For the lease vs buy and auto refi calculators:
- Auto loan APRs vary by credit score, vehicle age, lender, and state.
- Lease residual values, money factors, mileage allowances, and disposition fees are negotiable in some states and vary by manufacturer program.
- Total cost of leasing also depends on wear-and-tear charges at turn-in — items this calculator simplifies.
- Cars older than 10 years can be difficult to refinance. Lender approval depends on credit, vehicle age, mileage, and the loan-to-value ratio against the vehicle's current market value.
- Get actual loan terms in writing before signing.
Tax-implicated calculations
Where calculators reference tax brackets or after-tax outcomes:
- Tax outcomes depend on your specific income, filing status, state, and the tax law in effect at the time.
- Calculations use 2026 federal brackets and standard assumptions. They do NOT account for the Alternative Minimum Tax (AMT), the Net Investment Income Tax (NIIT), state tax, or many income phase-out provisions.
- For Roth conversions, qualified-plan rollovers, or any conversion-year-sensitive decision, consult a CPA before executing — the wrong-year conversion is a costly, often irreversible mistake.
Formula accuracy
The formulas used on this site are the standard published versions:
- PMT for amortizing loans (the same formula used by every bank, credit union, and mortgage calculator)
- Present value / future value for time-of-money comparisons
- Break-even = upfront cost ÷ ongoing benefit for refi and deductible comparisons
The math is correct. The inputs and assumptions are where uncertainty lives. We disclose every assumption in each calculator's "How this works" section and on the methodology page.
Limitations of this site
- We are not a licensed lender, broker, insurance agent, financial advisor, or tax preparer in any jurisdiction.
- The calculators cannot consider your full financial picture, dependents, healthcare situation, or career trajectory.
- The calculators cannot detect lender or carrier-specific tricks, special offers, or program-specific rules.
- For decisions over $25,000 in lifetime impact, you should consult at least one licensed professional in the relevant field.
Privacy
This site uses Cloudflare Web Analytics (cookieless, no personally-identifying data collected) for traffic measurement. If you submit an email address through any lead-magnet form, that email is processed by Formspree (a third-party form-handling service); we do not sell or share email addresses.
Corrections
If you find an error in any calculation, methodology, or fact stated on this site, please report it at the contact address on the about page. Confirmed errors are corrected within 7 business days and noted with a correction stamp.