Subpenny Pricing - API Documentation

For the general overview of fixed-point pricing and contract quantities across REST and WebSocket APIs, see Fixed-Point Representation.

Technical Specification

To enable subpenny precision, include tag 21005 in your Logon message:

Tag	Name	Description	Value
21005	UseDollars	Enable dollar-based price format	Y

Overview:

Legacy Format (Cents): Used when UseDollars(21005) is omitted or N. Prices given in whole cents. E.g. 72 cents = 72.
New Format (Dollars): Prices normalized to dollars with fixed precision (up to 4 decimal places).

In legacy cents mode, fractional Price(44) input is currently truncated when parsing the order. For example, 44=50.5 submits a 50-cent limit price. To submit 50.5 cents, set 21005=Y at Logon and send 44=0.5050.

Examples:

Cents	FIX Decimal	String Representation
1.23¢	Decimal(123, -4)	0.0123
72.5¢	Decimal(7250, -4)	0.725
99¢	Decimal(9900, -4)	0.99

Affected Tags:

Tag	Field Name	Description
6	AvgPx	Average price of fills
31	LastPx	Price of last fill
44	Price	Order limit price
132	BidPx	Quote bid price
133	OfferPx	Quote ask price

Sample Messages

8=FIXT.1.1|9=300|35=A|34=1|52=20250926-21:54:07.001|
96=QhA8659Mhygcm+xE/wb1m...|21005=Y|
                            ^^ Enable dollar format

8=FIXT.1.1|9=200|35=D|34=2|52=20250926-21:54:16.040|
38=100.0|40=2|44=0.7500|54=1|60=20250926-21:54:16.040|
              ^^ price
10=092|

8=FIXT.1.1|9=400|35=8|34=4|52=20250926-21:54:16.159|
6=0.6600|14=100|31=0.7000|32=60|38=100.0000|39=2|44=0.7500|
^^ avgPx        ^^ lastPx                        ^^ price

​Technical Specification

​Sample Messages

Technical Specification

Sample Messages