DR. WILLIAM GRANT DAY M.D.
NPI 1740745041
Allergy & Immunology in Portsmouth, VA

NPI Status: Active since January 31, 2019

Contact Information

620 JOHN PAUL JONES CIR STE 275
PORTSMOUTH, VA
ZIP 23708
Phone: (757) 953-2000

NPI Profile Information
Primary Taxonomy
Secondary Taxonomies
Secondary Locations
Medicare Participation & PECOS Status
NPI Validation
Other Providers Same Location
Frequently Asked Questions

Individual
Male
Allergy & Immunology
PECOS Enrolled

About WILLIAM DAY

This page provides the complete NPI Profile along with additional information for William Day, a provider established in Portsmouth, Virginia with a medical specialization in Allergy & Immunology. The healthcare provider is registered in the NPI registry with number 1740745041 assigned on January 2019. The practitioner's primary taxonomy code is 207K00000X with license number 0101271195 (VA). The provider is registered as an individual and his NPI record was last updated one year ago.

NPI: 1740745041
Provider Name: DR. WILLIAM GRANT DAY M.D.
Gender: Male
Entity Type: Individual
Location Address: 620 JOHN PAUL JONES CIR STE 275 PORTSMOUTH, VA 23708
Location Phone: (757) 953-2000
Mailing Address: 37 SERENITY LN SUFFOLK, VA 23433
Mailing Phone: (757) 613-6334
Is Sole Proprietor?: Yes
Enumeration Date: 01-31-2019
Last Update Date: 06-18-2025
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Location Map

Secondary Locations

8901 Rockville Pike
Bethesda, MD 20889
(757) 953-5000

Specialty - Primary Taxonomy

The NPI enumerator requires providers to submit at least one taxonomy code. A taxonomy code is a unique 10-character code that describes the healthcare provider type, classification, and the area of specialization. There could be only one primary taxonomy code per NPI record. For individual NPIs the license data is associated to the taxonomy code.

Classification: Allergy & Immunology
Taxonomy Code: 207K00000X
Type: Allopathic & Osteopathic Physicians
License No.: 0101271195
License State: VA
Taxonomy Description: An allergist-immunologist is trained in evaluation, physical and laboratory diagnosis, and management of disorders involving the immune system. Selected examples of such conditions include asthma, anaphylaxis, rhinitis, eczema, and adverse reactions to drugs, foods, and insect stings as well as immune deficiency diseases (both acquired and congenital), defects in host defense, and problems related to autoimmune disease, organ transplantation, or malignancies of the immune system.

Secondary Taxonomies

The provider has reported to the NPI enumerator additional taxonomy codes. Multiple taxonomy codes may represent subspecialties or other areas of specialization the provider maybe licensed to practice.

No.	Taxonomy Code	Type	Classification / Specialization	License No. (State)
1	207R00000X	Allopathic & Osteopathic Physicians	Internal Medicine	0101271195 (VA)

Medicare Participation & PECOS Enrollment Status

William Day is enrolled in PECOS and is eligible to order or refer health care services for Medicare patients. The provider is eligible to order or refer: Part B Clinical Laboratory and Imaging, Durable Medical Equipment (DME), a Home Health Agency (HHA) and Power Mobility Devices.

What is PECOS?
PECOS is the online Medicare enrollment management system or Provider, Enrollment, Chain and Ownership System. The PECOS system is a database of providers who have registered with CMS as providers or suppliers. PECOS is the primary source of information about verified Medicare professionals. Providers that want to participate in this program need to enroll in PECOS with their NPI number to avoid denied claims.

Is the provider registered in PECOS? Yes
Eligible to Order or Refer Part B Clinical Laboratory and Imaging: Yes
Eligible to Order or Refer Durable Medical Equipment (DMEPOS): Yes
Eligible to Order or Refer a Home Health Agency (HHA): Yes
Eligible to Order or Refer Power Mobility Devices: Yes

NPI NPI Number Validation

How NPI Validation Works

The NPI validation process uses the ISO-standard Luhn algorithm, a mathematical "handshake", to ensure that a provider's 10-digit ID is authentic and free of common typing errors.

To verify the NPI 1740745041, we treat the final digit (1) as the Check Digit—the target answer we need to reach. The process begins by taking the first nine digits and adding a constant value of 24, which accounts for the "80840" prefix required for all U.S. health identifiers. We then double every other digit starting from the right and sum the individual digits of those results together. For this specific NPI, that total comes to 59. The final step is to find the difference between that total and the next multiple of ten (60 - 59 = 1).

Digit-by-digit view

Use the first nine digits for the calculation. Starting from the right, double every other digit. The last digit is the check digit and is not part of the calculation.

Pos 1

Doubled → 2

Pos 2

Unchanged

Pos 3

Doubled → 8

Pos 4

Unchanged

Pos 5

Doubled → 14 → 1 + 4

Pos 6

Unchanged

Pos 7

Doubled → 10 → 1 + 0

Pos 8

Unchanged

Pos 9

Doubled → 8

Check

Target digit

Regular digit Doubled digit Check digit

Step 1: Double every other digit from the right

Starting with the rightmost digit of the first nine digits, double every other value. If doubling creates a two-digit number, add those digits together.

1 → 2 4 → 8 7 → 14 → 5 5 → 10 → 1 4 → 8