Medical Billing Resources — Denial Codes, Tools & Guides

Billing Knowledge, Free

This resource center is written and maintained by the LegitMedBilling team — the same people who work claims, denials, and credentialing for practices every day. Everything here is free to use: reference guides for the codes you see on remittances, and working tools for the math you do at the front desk and in the billing office. New sections and pages are added weekly.

Denial Code Library

Plain-English guides to CARC denial codes — what CO-45, CO-16, CO-97 and others mean, how to fix them, and appeal wording that works.

Billing Calculators & Tools

Copay, coinsurance, denial cost, and Days in A/R calculators — free, instant, no signup.

Billing & RCM Articles

In-depth guides on denials, credentialing, specialty billing, and growing a practice.

Place of Service (POS) Codes

Plain-English POS code reference — office, telehealth, hospital, ASC and more — and how each one changes what you get paid.

CPT Modifier Library

Modifier 59, 25, the X-subset and more — when each applies, audit risks, and the denials they cause and cure.

Insurance Payer Guides

UnitedHealthcare and more — typical filing limits, appeal deadlines, portals, payer IDs, and the denial patterns each payer is known for.

CPT Code Guides

Plain-English guides to the codes on your claims — E/M level rules, documentation, typical pay, and the denials each code attracts.

Medical Billing Glossary

45+ billing and insurance terms in plain English — from allowed amount to write-off, with links to deeper guides and calculators.

Billing Resources