CAS vs EIS: two different things that work together
“CAS” and “EIS” get used interchangeably, and that confusion trips up agencies preparing for the e-invoicing mandate. They are not the same: CAS registration is how the BIR recognizes your system; the EIS is how structured invoice data is issued and reported. You need both to fit together.
Key Takeaways
- CAS = Computerized Accounting System registration — the BIR recognizes your system and issues an Acknowledgement Certificate (Section 237).
- EIS = the Electronic Invoicing System — the platform that receives structured invoice data for electronic sales reporting (Section 237-A).
- CAS is about registering the system; EIS is about issuing and reporting the structured invoice through it.
- “EIS-ready” software does both: registers as a CAS and produces EIS-format, signed invoices — neither alone is enough.
What is CAS registration?
CAS registration is the BIR process for recognizing a Computerized Accounting System (or its components). Under RMC 5-2021 it is done through the ORUS portal and results in an Acknowledgement Certificate — which replaced the old Permit to Use — issued within three working days of complete documents, with no system demo required.
CAS registration is grounded in Section 237 of the Tax Code (issuance of invoices from a registered system). It is the “your system is recognized” step.
What is the EIS?
The EIS (Electronic Invoicing System) is the BIR platform that receives invoice data electronically. It is grounded in Section 237-A (electronic sales reporting). A covered taxpayer issues structured invoice data and, when the receiving system is in place, transmits it to the EIS — the “report the invoice” step.
How do CAS and EIS relate?
They are sequential, not alternatives. You register your system as a CAS so the BIR recognizes it, and that system must be able to issue structured EIS-format invoices and report them to the EIS when required. CAS is the registration; EIS is the issuance-and-reporting that flows through it.
| Aspect | CAS registration | EIS |
|---|---|---|
| What it is | Registration of your computerized system | Platform for structured invoice data |
| Tax Code basis | Section 237 (issuance) | Section 237-A (electronic sales reporting) |
| Artifact | Acknowledgement Certificate | Certified transmission of EIS-format data |
| Question it answers | “Is my system recognized?” | “Is my invoice issued and reported correctly?” |
| Timing | Register now | Real-time transmission phased in (separate RR) |
For the technical side of the EIS invoice, see the EIS JSON / JWS format; for the registration steps, how to become EIS-ready; and to avoid the marketing trap, “EIS-ready” vs “BIR-accredited”.
Frequently asked questions
CAS (Computerized Accounting System) registration is how the BIR recognizes your computerized invoicing/accounting system — it issues an Acknowledgement Certificate. The EIS (Electronic Invoicing System) is the BIR platform that receives structured invoice data. CAS is about registering your system; EIS is about issuing and reporting structured invoices through it.
In practice, yes. You register your system (CAS Acknowledgement Certificate) so the BIR recognizes it, and that system must be able to issue structured e-invoices and, when required, report them to the EIS. One is the registration; the other is the issuance-and-reporting.
Not exactly. CAS registration recognizes your system with an Acknowledgement Certificate. “EIS-ready” means the system can also produce the structured invoice data (JSON), sign it, and transmit to the EIS when required. A system can be CAS-registered and still need EIS capability — good software provides both.
You move billing onto a system capable of structured invoicing, register it as a CAS to get the Acknowledgement Certificate, and ensure it can issue EIS-format invoices. Real-time transmission to the EIS follows once the BIR's receiving system is fully in place under a separate regulation.
One system, CAS-registered and EIS-ready.
NexusWorkforce issues structured, EIS-format invoices and registers as a CAS — the registration and the issuance handled together, from the same platform that runs payroll and DTR.
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