Medical Billing 101 is a free US guide to claim denials, coding and patient billing. It is written by Manikandan J, CPC, CRCR, who has more than 10 years of experience in US medical billing. Every guide checks codes and rules against official sources, such as the X12 code lists and CMS manuals, and links to them.
Key takeaways
- One author writes or reviews every page: Manikandan J, CPC, CRCR.
- He has worked in US medical billing at athenahealth, Omega Healthcare, UnitedHealthcare, Blue Cross Blue Shield and Access Healthcare.
- Code wording is quoted from X12. Medicare rules link to CMS.
- The site is free and for education only. It is not legal or billing advice for your practice.
Who writes Medical Billing 101
Medical Billing 101 is written by Manikandan J. He has more than 10 years of experience in US medical billing and revenue cycle work. He has worked at athenahealth, Omega Healthcare, UnitedHealthcare (UHC), Blue Cross Blue Shield (BCBS) and Access Healthcare. You can see his work history on LinkedIn.
He holds two industry credentials. CPC is the Certified Professional Coder credential. CRCR is the Certified Revenue Cycle Representative credential.
| Credential | Issued by | What it covers |
|---|---|---|
| CPC (Certified Professional Coder) | AAPC | Coding of provider services with CPT, HCPCS Level II and ICD-10-CM codes |
| CRCR (Certified Revenue Cycle Representative) | HFMA, the Healthcare Financial Management Association | Revenue cycle operations, including patient access, patient financial services and compliance |
Who the site is for
The site has two kinds of readers. The first is billers, coders and provider offices who work denied claims. The second is insured patients who got a denial or a confusing bill. For example, a biller can look up CO-197 to see what the payer wants. A patient can read our patient guides to learn what to ask the insurer.
- Denial code library: what each code means and how to fix it.
- Free tools: an appeal letter generator and a timely filing calculator.
- Patient guides: plain-English help with denials and bills.
Why this site exists
A denial often shows up as a short code on a remittance or an Explanation of Benefits. A CARC is the standard code a payer uses to say why it paid a claim differently from how it was billed. The X12 CARC list names the problem in a few words, but it rarely says what to do next. The answers sit in CMS manuals and payer policies, which are written as reference, not as steps.
Medical Billing 101 closes that gap between official documentation and everyday denial management. Each guide explains what a code means and why payers use it. Then it shows how to fix and resend the claim or appeal it, and what a patient can ask.
How we check our guides
Every guide follows our editorial policy. In short:
- Code wording is quoted word for word from the X12 CARC and RARC lists.
- Medicare rules link to the CMS manual or Medicare contractor page they come from.
- When a rule comes from one payer, we name that payer. We don’t call it a national rule.
- We don’t publish numbers that no official source states. Worked examples are marked as examples.
- Reviewed pages show a “Last reviewed” date.
Manikandan J writes or reviews every page before it goes live.
Contact and corrections
Think a page is wrong or out of date? Email info@medicalbilling101.com with the page and your source. You can also reach Manikandan on LinkedIn. We check each report against the official source and fix the page if it is wrong. See the contact page for what to include.
FAQ
Who writes Medical Billing 101?
Manikandan J, CPC, CRCR. He writes or reviews every page on the site.
Is Medical Billing 101 free?
Yes. The guides and tools are free to use, with no sign-up.
Can you give advice on my claim?
No. The site is for education. For your own claim, check with the payer, your billing office or a qualified professional.
Disclaimer
The information on Medical Billing 101 is for education only. It is not legal, medical or financial advice. Payer contracts and policies differ, so check the rules for your claim with the payer before you bill or appeal. Read our full disclaimer.
Last reviewed by Manikandan J, CPC, CRCR on October 14, 2026.