Methodology

FeeFriction publishes estimators, not quotes. Every calculator states core assumptions on its page. This document summarizes the shared math.

Amortizing loans (personal / auto)

Fixed-payment tools use standard amortization: payment = P · r(1+r)^n / ((1+r)^n − 1) with monthly rate r and n periods (unless r = 0). Origination fees may reduce cash received while interest accrues on the note amount when modeled that way.

Refinance break-even

Months ≈ closing costs ÷ monthly payment savings, holding remaining term constant so the rate change is isolated.

Credit cards

Month-by-month simulation applies monthly APR/12 then subtracts payment. The “minimum path” uses a simplified illustration (~2% + interest style), not every issuer’s exact formula.

401(k) fee drag

Annual model: add contribution, then grow by (gross return − fee). Return is user-set. Not a market forecast.

Paycheck take-home

Educational federal bracket sketch + FICA-style rates + a flat state rate you enter. Not IRS Publication 15-T withholding tables, not a W-4 tool, and not tax advice. Verify against your payroll stub.

HELOC interest

Interest-only estimate on a constant drawn balance. Variable indexes, fees, and amortizing repayments need product disclosures.

Bank fee leak / remittance

Arithmetic totals of fees you enter. FX markup is a percentage gap vs mid-market in USD terms — not a live quote engine.

Inflation vs raise

Compares nominal compounding of raises vs an assumed CPI path to approximate real purchasing power.

Structured data policy

We use WebPage, Article, FAQPage, BreadcrumbList, Organization, Person, and SoftwareApplication (free, no Offer). We intentionally avoid Product / AggregateRating / merchant shipping schema without real reviews — those created GSC enrichment warnings on earlier network sites.

Updates

Editorial review when tax/wage-base references or product norms change materially. Dates appear on trust pages and author boxes.