BIR CAS vs BIR EIS — two obligations, constantly confused
One is permission to keep your books on software. The other is an ongoing data feed to the BIR. Most businesses need both, and the order you tackle them in changes the cost.
The short version
| CAS registration | EIS e-invoicing | |
|---|---|---|
| What it is | BIR approval of your accounting system | Ongoing transmission of invoice data to the BIR |
| Frequency | One-off, plus amendments when the system materially changes | Continuous — within three calendar days of every transaction |
| Output | Acknowledgement Certificate / Permit to Use | Accepted transmissions, logged |
| Who assesses it | Your Revenue District Office, via a live demonstration | The EIS platform, automatically, on every submission |
| Fails because of | Weak flowcharts, unreconciled sample reports, no demonstrable audit trail | Missing buyer TINs, malformed JSON, signature or connection errors |
CAS registration in detail
A Computerized Accounting System is any software you use to keep books of account electronically. Before you rely on it for statutory records, it must be registered. The application is a documentation and demonstration exercise:
- System description — how entries are captured, processed, posted and stored, including security and access controls
- Functional flowcharts — per cycle: procure to pay, order to cash, record to report, fixed assets
- Sample output reports — specimen books of account, journals, ledgers, invoices and receipts
- Live demonstration to RDO evaluators, tracing transactions through to statutory reports
The system must maintain an immutable audit trail and produce reports that reconcile to the general ledger without manual assembly. Those two properties are what evaluators actually probe.
EIS e-invoicing in detail
The Electronic Invoicing System receives invoice data directly from taxpayers' systems under RR 11-2025, extended by RR 26-2025, resting on Sections 237 and 237-A of the Tax Code as amended by the CREATE MORE Act. Requirements: structured JSON, digital signature, system-to-system API transmission, three-day window, ~54 mandatory data elements.
Where they interlock — and why it matters commercially
Holding a registered CAS places you inside the first EIS compliance group, with the 31 December 2026 deadline, regardless of your revenue. That is the connection most businesses miss.
It cuts the other way too. Building EIS transmission on a system that was never properly registered creates a documentation gap: you are feeding the BIR data from software it has not approved for your books. Neither obligation is safely handled in isolation.
The order that costs least
- Get the system right first. Both obligations assume a system with an immutable audit trail and clean, reconcilable reporting. Remediating that later means redoing both.
- Clean the data. Buyer TINs, item master, VAT treatment. CAS needs it for credible sample outputs; EIS needs it to pass validation. One cleanup serves both.
- Register the CAS. Documentation and demonstration, with the system already behaving correctly.
- Connect EIS transmission. Parallel run, then cut over.
Businesses that invert steps 3 and 4 usually end up amending the CAS filing, because connecting transmission materially changes the registered system.
Common mistakes
- Treating EIS as a print-format change. It is a data-transmission obligation.
- Assuming a CAS permit covers e-invoicing. It does not — it does the opposite, by pulling you into the first compliance group.
- Buying middleware before checking the ERP. If the ERP can generate, sign and transmit natively, a middleware layer adds a failure point and a second reconciliation.
- Leaving branches out. Both obligations reach branch operations.
This is a planning summary of publicly available regulation, not tax advice.
Where to go next
Work out whether the deadline applies to you with the four-question checklist, read the detail on CAS registration and EIS compliance, or see how both are handled inside a Business Central implementation.
Frequently asked questions
Do we need both CAS registration and EIS compliance?
Which should we do first?
Does a CAS Permit to Use expire?
Can one project cover both obligations?
Want this checked against your actual situation?
Send us your BIR registration type and what you run today. You will get a direct answer, not a discovery call invitation.