Precision modeling is the bedrock of fiscal strategy. We turn volatile tax rules, APR structures, and merchant interchange equations into transparent, actionable calculators.
New York, NY • Lead Financial Analyst & Tax Technology Editor
CPA, M.S. Finance (NYU Stern)
David Miller is a Certified Public Accountant (CPA) and veteran financial modeler. Prior to joining Infinix Calculators as Lead Financial Editor, David spent over a decade advising e-commerce enterprises, multi-state retailers, and tech startups on sales tax nexus compliance, payroll gross-up structures, and credit card processing fee mitigation.
At Infinix Calculators, David oversees the mathematical accuracy of all financial calculators, including Buy Now Pay Later (BNPL) installment interest engines, reverse merchant processing fee equations, and mortgage amortization algorithms.
His technical articles on sales tax sourcing, payroll bonus withholding formulas, and payment processor interchange math have helped thousands of small business owners protect their profit margins.
Learn the math, strategies, and interactive games to pay down your mortgage faster. Compare prepaying vs. investing, and track your Savings Score.
Calculate sales tax rates by ZIP code with our Avalara tax guide. Explore state, county, and local rates for San Francisco 94105, Houston, and Chicago.
Master California sales tax sourcing guidelines and local district surtaxes. Learn rules for ZIP code 94105, San Francisco county, and grocery food tax.
Calculate Square credit card processing fees for swiped, keyed, and invoice payments. Learn the reverse gross-up formula to net 100% of your invoice value.
Discover the complete Infinix Calculator suite for business finance, construction materials, health metrics, and math. Free precision tools for fast decisions.
Compare Affirm BNPL installment loans against revolving credit card debt. Explore fixed simple interest rates, credit score impacts, and payment control.
Learn how Affirm affects your credit score. Understand soft credit inquiries, monthly loan reporting, payment history benefits, and hard pull risks.
Discover how Affirm works: 0% interest Pay-in-4 biweekly plans vs 3, 6, 12, or 24-month monthly installment loans. Learn approval rules and terms.
Learn proven strategies to escape Buy Now Pay Later debt traps. Discover how early payoff works with zero prepayment penalties on Affirm installment loans.
Compare Affirm vs Klarna vs Afterpay BNPL apps. Explore 0% interest options, late fee policies, soft vs hard credit checks, and credit bureau reporting.
Explore Avalara AvaTax pricing tiers, transaction overage charges, and multi-year contract traps. Compare top alternatives like TaxJar, Anrok, and Numeral.
Learn how to calculate reverse sales tax with simple step-by-step formulas. Extract original pre-tax prices and sales tax from receipts and invoices.
Explore 2026 state sales tax rates, local surtaxes, economic nexus rules, zero sales tax states (NOMAD), and city rates for CA, TX, FL, NY, CO, and IL.
Technical sales tax integration guide for WooCommerce, NetSuite (SuiteTax vs Avalara), Odoo, and Shopify. Learn remote seller address validation math.
Discover the cheapest sales tax filing software for e-commerce. Compare TaxJar, Anrok, Numeral, Quaderno, open-source tax APIs, and CPA filing fees.
An in-depth merchant cost breakdown evaluating whether Square's 2.6% + $0.10 flat rate processing fees are worth it compared to Stripe, Toast, Clover, and Interchange-Plus pricing.
Learn how small business owners pass Square fees to customers legally. Explore credit card surcharges, state legal restrictions, cash discounts, and compliance rules.
Free Square processing fee calculator to compute exact credit card transaction fees (2.6% + $0.10 in-person, 2.9% + $0.30 online). Learn how to calculate net payouts.
Discover how Affirm calculates your spending power, why approved loan limits fluctuate, soft credit checks, and when down payments are required.
Demystify Affirm's interest calculation formula. Compare simple interest vs compounding credit card APR, 3 to 36 month loan terms, and total finance costs.
Learn how paying off your Affirm loan early or making extra partial payments cancels future simple interest with zero prepayment penalties.
Uncover how merchant subsidies fund 0% APR promotional plans on Apple and Samsung products, down payment interest adjustments, and zero fee policies.
Detailed guide on stores accepting Affirm (Amazon, Walmart, Best Buy, Home Depot, eBay, Apple), plus rules for paying rent, utility bills, gift cards, and car rentals.
Guía exhaustiva en español sobre el funcionamiento de Affirm BNPL: préstamos Pay in 4 al 0% APR, cuotas mensuales, revisiones de crédito y tarjeta de débito Affirm.
Master paycheck gross-up calculations for employee bonuses, relocation stipends, fringe benefits, and nanny salaries. Learn the reverse tax equation and state-by-state payroll rules.
Understand Affirm interest rate calculations (0% to 36% APR). Learn simple vs compound interest, Pay-in-4 biweekly options, credit score impacts, and early payoff savings.
Game out your mortgage payoff timeline! Explore interactive mortgage games, extra principal overpayment math, 30-year vs 15-year equity curves, and PITI affordability tools.
Calculate credit card balance transfer fee math (3% vs 5%). Compare 0% APR promotional windows against high interest rates, payoff timelines, and credit score impacts.
Gamify your homebuying journey. Learn how mortgage calculator games, amortization simulators, and financial interactive scenarios help buyers master interest rates and budgeting.
Detailed sales tax rate breakdown for ZIP code 94105 in San Francisco, California. Learn state, county, and local district rates, reverse tax math, and automated Avalara API lookup rules.
