How to Calculate a DEA Number: Format and Check Digit
Updated
A DEA number has a check digit built into it, which means you can spot an invalid one with nothing but arithmetic. That is why this shows up on the PTCE: it is a rule you either know or you do not, and it takes about fifteen seconds to apply.
This page covers the format and the calculation. It sits in the Federal Requirements domain, which is 18.75% of the 2026 exam.
The format
Every DEA number is two letters followed by seven digits. Take AB1234563:
- A is the registrant type.
- B is normally the first letter of the registrant's last name.
- 1234563 is the registration number, and the final 3 is the check digit calculated from the six before it.
What the first letter tells you
| Letter | Registrant type |
|---|---|
| A, B, F | Hospital, clinic, practitioner, teaching institution, or pharmacy. A is the oldest series, B and F are later ones. The letter says nothing about the registrant beyond the series they were issued in. |
| G | US Government, including military, Department of Defense, and Public Health Service registrants. |
| M | Mid-level practitioner: nurse practitioner, physician assistant, optometrist, and similar. |
| P, R | Manufacturer, distributor, researcher, analytical lab, importer, exporter, reverse distributor, or narcotic treatment program. |
| X | Formerly a DATA-waived practitioner prescribing buprenorphine for opioid use disorder. No longer issued: the MAT Act removed the X-waiver requirement, so X numbers appear only on historical records. |
The check digit calculation
Four steps, using only the seven digits:
- Add the 1st, 3rd and 5th digits.
- Add the 2nd, 4th and 6th digits, then double that sum.
- Add the two results together.
- The units digit of that total must equal the 7th digit.
Worked example: AB1234563
Digits are 1 2 3 4 5 6, with 3 as the check digit.
- Odd positions: 1 + 3 + 5 = 9
- Even positions: 2 + 4 + 6 = 12, doubled = 24
- Total: 9 + 24 = 33
- Units digit of 33 is 3, which matches the check digit. Valid.
A second example: BM4837297
Dr. Martinez, a practitioner, so B for the registrant type and M for the surname. Digits are 4 8 3 7 2 9, with 7 as the check digit.
- Odd positions: 4 + 3 + 2 = 9
- Even positions: 8 + 7 + 9 = 24, doubled = 48
- Total: 9 + 48 = 57
- Units digit is 7, matching the check digit. Valid.
Why doubling matters
A plain sum would miss transposed digits, and transposition is the most common way a number gets copied wrong. Doubling alternate positions makes the order matter. Swap the first two digits of our first example so 123456 becomes 213456:
- Odd positions: 2 + 3 + 5 = 10
- Even positions: 1 + 4 + 6 = 11, doubled = 22
- Total: 32, units digit 2, not 3. The swap is caught.
What a valid check digit does not prove
This is the part exam questions like, because the intuitive answer is wrong. A valid check digit tells you the number is internally consistent. It does not tell you the number is real. Anyone who knows the formula can construct a number that passes, which means the check catches honest mistakes and lazy forgeries, and nothing more.
A number that passes the arithmetic can still be:
- Never issued by DEA at all.
- Issued to a different prescriber than the one named on the prescription.
- Expired, suspended, or surrendered.
- Outside the prescriber's authority, for example a mid-level practitioner writing beyond what their state permits.
Confirming any of those requires checking DEA registration records, not arithmetic. A technician runs the check and escalates anything that fails or looks odd; what happens next is the pharmacist's decision.
Common exam traps
- Doubling the wrong group. You double the even-position digits (2nd, 4th, 6th), not the odd ones. Getting this backwards produces a plausible wrong answer, which is exactly why it is offered as a distractor.
- Using the whole total instead of its units digit. The check digit is a single digit, so 33 gives you 3.
- Assuming the second letter must match the surname. It usually does, but name changes and DEA's use of 9 in that position make it a soft check.
- Treating X numbers as current. The MAT Act removed the X-waiver requirement for prescribing buprenorphine for opioid use disorder, so X numbers are historical. Study material written before that change still presents them as live.
Frequently asked questions
How do you calculate a DEA number?
You do not calculate the whole number, you calculate and verify its last digit, which is a check digit. Add the first, third and fifth digits together. Add the second, fourth and sixth digits together and double that sum. Add the two results. The units digit of the total must match the seventh digit of the DEA number. If it does not, the number is invalid.
What is the format of a DEA number?
Two letters followed by seven digits, for example AB1234563. The first letter identifies the registrant type. The second letter is normally the first letter of the registrant's last name, or of the business name for an organisation. The seven digits are the registration number, and the last of those seven is a check digit derived from the first six.
What does the second letter of a DEA number mean?
It is usually the first letter of the registrant's surname, so Dr. Martinez would typically have a DEA number whose second letter is M. Treat this as a soft check rather than a hard rule. A registrant who changed name, for example after marriage, may keep a number whose second letter no longer matches, and DEA has used a 9 in that position for some registrants. A mismatch is a reason to verify, not proof of forgery.
Why does the check digit double the even-position digits?
Doubling every second digit is what lets the formula catch transpositions. If the check were a plain sum, swapping two adjacent digits would not change the total and the error would pass unnoticed. Weighting alternate positions differently means a swap changes the result. Swapping the first two digits of 123456 turns it into 213456, and the check digit moves from 3 to 2, so the error is caught.
Does a valid check digit mean the DEA number is real?
No, and this is the trap most often tested. The check digit proves only that the number is internally consistent. Anyone who knows the formula can build a fake number that passes it. A valid check digit rules out typos and casual invention; it does not confirm that the number was ever issued, that it belongs to the prescriber named on the prescription, or that the registration is still active. Confirming those requires verifying against DEA registration records.
Can a pharmacy technician verify a DEA number?
A technician can and routinely does run the arithmetic check and flag anything that fails, which is exactly the sort of task the exam expects you to handle. Deciding what to do about a suspicious prescription is the pharmacist's call, not the technician's.
Keep studying
DEA number validation is one of several federal rules the exam tests as a procedure rather than a fact. Drill the rest with the federal requirements quiz and the controlled substance dispensing practice set. The controlled substance schedules reference covers which drugs a DEA registration actually authorises, and the full Federal Requirements domain guide puts both in context.
PTCB Quiz Prep is an independent study resource, not affiliated with the Pharmacy Technician Certification Board or the Drug Enforcement Administration. This page is exam reference framing, not legal advice.