Medical billing resources: guides, codes, rules, payers and tools
Our billing resources are split into libraries, and each one answers a different kind of question. Use a guide for a decision, the code library for a code, the rules for a limit, a payer guide for one payer and the glossary for a term.
Written by Salman Saeed, CEO and Co-Founder · Reviewed by a Certified Medical Coder · Last reviewed October 2026
New guides, posts and news
Blog
Payers and states
Blog
Blog
Denials and A/RBlogWhich resource answers my billing question?
Start with the question, not the section name. The table matches common questions to the library that answers them.
| If you need to | Go to | What you find there |
|---|---|---|
| Make a billing decision, such as choosing a billing partner | Guides | Steps, forms and checklists for one decision. |
| Look up a CPT, HCPCS, modifier, denial or revenue code | Code library | One page per code, grouped for billers. |
| Check a filing limit, coding edit or payment rule | Rules | One page per billing rule. |
| See how one payer pays, appeals and denies | Payer guides | Filing limits, appeals, portals and denials, tied to the payer's own manual. |
| Check what a billing term means | Glossary | Plain definitions of the terms the pages use. |
| Work out a deadline, KPI or billing cost | Tools | Calculators for NSA deadlines, timely filing, A/R days, collection rate and billing cost. |
| Fix one specific billing problem | Blog | One post per question, newest first. |
| Read what changed in a CMS or Federal Register rule | News | Dated rule changes from official sources. |
The libraries link to each other. A guide points to the rule and code pages behind it, and a code page points to the payers and specialties that use it. State rules are in the state pages, and system-specific work is on the EHR pages.
How are the resources sourced and kept current?
Codes, rules, deadlines and fees on every page come from official sources such as CMS, the Federal Register, the eCFR and the payer's own provider manual. Each page lists those sources and a last-reviewed date.
Our editorial policy describes who writes and reviews the pages and how corrections are handled. To talk through your own claims, book a call.
Common questions
Straight answers from the team that does the work.
Ask a billing lead directly. A 20-minute call, Monday to Friday, 9am to 5pm Eastern.
01What billing resources does Nucleus Align publish?
We publish guides, a code library, a rules library, payer guides, a glossary, billing tools, a blog and a news page. Each covers a different kind of question. Guides explain decisions, the code and rule pages give the detail, and the news page tracks rule changes from CMS and the Federal Register.
02Where do I look up a medical billing code?
Use the code library, which has pages for CPT, HCPCS, modifier, denial, revenue and ICD-10-CM codes. For a term you do not recognise on a page, the glossary defines it in plain words. For a denial you are working, the blog has a post for common denial codes such as CO-16 and CO-97.
03Where can I find a payer's filing limit or appeal steps?
Open the payer guides. Each one covers the payer's filing limits, appeal levels, portal and common denials, and ties them to the payer's own provider manual. For limits set by law or by Medicare, the rules library has the matching rule page.
04Are there billing calculators?
Yes. The tools page has five calculators for NSA deadlines, timely filing, A/R days and denial rate, collection rate, and the cost of in-house versus outsourced billing. Run them with your own figures, and use the matching guide to read the result.
05Can I get billing rule changes by email?
Yes. Use the sign-up form on this page to get billing rule changes by email. See our privacy policy for how we handle it. The same changes are always listed on the news page, which you can read without signing up.
06How do I know the resources are current?
Every page shows a last-reviewed date, which is the day someone last checked it against its official sources. When a source changes, the affected pages are re-checked and re-dated. If a date looks old, confirm the numbers at the source linked on the page.
Not sure where to look?
Book a call and a billing lead will point you to the right page.