Date of Birth (0x2A85): byte layout
GATT characteristic · org.bluetooth.characteristic.date_of_birth · read from the Bluetooth SIG’s repository on 2026-10-17 · commit 408f4a0 (2026-10-14)
Date of Birth is Bluetooth GATT characteristic 0x2A85, org.bluetooth.characteristic.date_of_birth in the Bluetooth SIG's assigned numbers. The SIG's GATT Specification Supplement file lays its value out as 3 fields: Year, Month and Day. Every field has a fixed size, 4 octets in all. The SIG's User Data permitted-characteristics list includes it.
- UUID
- 0x2A85
- Identifier
org.bluetooth.characteristic.date_of_birth- The SIG’s description
- The Date of Birth characteristic is used to represent the date of birth of a user as defined by the Gregorian calendar.The structure of this characteristic is defined below.
- Service the SIG’s files tie it to
- User Data (0x181C) — listed in uds_permitted_characteristics.yaml
- Source file
- gss/org.bluetooth.characteristic.date_of_birth.yaml
Byte layout: 3 fields
In the order the SIG’s structure lists them. Type and size are as published; sizes count octets except where a struct is marked as sized in bits. The offset is printed only where every earlier field has a fixed size; where an earlier field can be absent or vary, the cell names what it depends on. “Present when” is read from the field’s own “Present if” line, shown in full in the field notes below.
Field notes
Each field’s text in the SIG’s file, line by line.
- Year uint16 · 2
- Unit: org.bluetooth.unit.time.year The Year is an integer value. Minimum value: 1582 Maximum value: 9999 In addition to the above range, a special value is defined: 0 = Year is not known
- Month uint8 · 1
- See Month.
- Day uint8 · 1
- Unit: org.bluetooth.unit.time.day The Day is an integer value. Minimum value: 1 Maximum value: 31 In addition to the above range, a special value is defined: 0 = Day of Month is not known
Flags and value tables
The definitions the SIG’s file gives for its fields, every row as published. On a flags table the last column lists the fields whose “Present if” line names that bit.
Month
The values of this field are defined below.
| Value | Description |
|---|---|
| 0 | Month is not known |
| 1 | January |
| 2 | February |
| 3 | March |
| 4 | April |
| 5 | May |
| 6 | June |
| 7 | July |
| 8 | August |
| 9 | September |
| 10 | October |
| 11 | November |
| 12 | December |
| 13–255 | Reserved for Future Use |
Guides on this site
No guide on this site names 0x2A85 yet. The connected-devices guides cover pairing, subscribing and testing for the device types they do name.
Questions
- What is the UUID of the Date of Birth characteristic?
- 0x2A85. The Bluetooth SIG's characteristic_uuids.yaml lists Date of Birth as 0x2A85 with the identifier org.bluetooth.characteristic.date_of_birth. The SIG's User Data (0x181C) permitted-characteristics list includes it.
- Are any Date of Birth fields optional?
- No. Every field in the SIG's structure has a size that cannot be zero: Year (uint16, 2), Month (uint8, 1) and Day (uint8, 1).
- What units does Date of Birth use?
- The SIG's text names a unit for 2 of the 3 fields: Year: time (year) (org.bluetooth.unit.time.year); Day: time (day) (org.bluetooth.unit.time.day).
- How many bytes is a Date of Birth value?
- 4 octets. Every field has a fixed size in the SIG's structure: Year at offset 0 (uint16, 2), Month at offset 2 (uint8, 1) and Day at offset 3 (uint8, 1).
- Which values does the Date of Birth Month table define?
- 0: Month is not known; 1: January; 2: February; 3: March; 4: April; 5: May; 6: June; 7: July; 8: August; 9: September; 10: October; 11: November; 12: December. The other rows are reserved for future use or carry no text.
Source
Read on 2026-10-17 from gss/org.bluetooth.characteristic.date_of_birth.yaml and assigned_numbers/uuids/characteristic_uuids.yaml in the Bluetooth SIG’s public repository (branch main, commit 408f4a0, committed 2026-10-14), by scripts/fetch-bluetooth-gatt.mjs. The file’s notice says it is proprietary to Bluetooth SIG, that furnishing it grants no licence, and that it is subject to change without notice; it is © Bluetooth SIG, Inc., and its text is quoted here for identification. Generated by AIFitnessAPI, which is not affiliated with Bluetooth SIG; the SIG’s file remains the authority. The full notice and the conventions used on these pages are on the reference hub.