MaturityDay (FIX tag 205)

DayOfMonthFIX 4.2

MaturityDay (tag 205) is a DayOfMonth field defined in FIX 4.2. It appears in 26 message types, always optionally.

At a glance

Tag: 205
Name: MaturityDay
Datatype: DayOfMonth (int)
Dialects: FIX 4.2
Messages: 26

What the specification says

Day of month used in conjunction with MaturityMonthYear to specify the maturity date for SecurityType=FUT or SecurityType=OPT.

Descriptions are quoted from the FIX Orchestra sources under the Apache 2.0 licence.

A real message using tag 205

OrderSingle · FIX 4.2

Tag	Field	Wire value	Meaning
8	BeginString	FIX.4.2
9	BodyLength	133
35	MsgType	D	Order Single
49	SenderCompID	BOARTEAM
56	TargetCompID	COUNTERPARTY
34	MsgSeqNum	2
52	SendingTime	20240101-12:00:00.000
11	ClOrdID	ORD-10042
21	HandlInst	1	Automated execution order, private, no Broker intervention
55	Symbol	EUR/USD
205	MaturityDay	1
54	Side	1	Buy
60	TransactTime	20240101-12:00:00.000
40	OrdType	1	Market
10	CheckSum	121

Edit and decode it yourself

Shown with | separators for readability. On the wire FIX uses SOH (0x01), an invisible control byte — and because BodyLength and CheckSum are computed over the actual bytes, the two forms have different checksums. Both are valid and both decode here.

Open in the full decoder →

Generated from the FIX 4.2 dictionary and verified at build time: it parses and validates with no issues. Open the decoder to try your own message.

Where tag 205 appears

Requiredness is a property of the message, not of the field: the same tag can be optional in one message and conditionally required in another.

Message	MsgType	Requiredness	Where in the message
Advertisement	7	Optional	directly on the message body
Allocation	J	Optional	directly on the message body
DontKnowTrade	Q	Optional	directly on the message body
Email	C	Optional	directly on the message body
ExecutionReport	8	Optional	directly on the message body
IOI	6	Optional	directly on the message body
ListStrikePrice	m	Optional	directly on the message body
MarketDataIncrementalRefresh	X	Optional	directly on the message body
MarketDataRequest	V	Optional	directly on the message body
MarketDataSnapshotFullRefresh	W	Optional	directly on the message body
MassQuote	i	Optional	directly on the message body
News	B	Optional	directly on the message body
OrderCancelReplaceRequest	G	Optional	directly on the message body
OrderCancelRequest	F	Optional	directly on the message body
OrderList	E	Optional	directly on the message body
OrderSingle	D	Optional	directly on the message body
OrderStatusRequest	H	Optional	directly on the message body
Quote	S	Optional	directly on the message body
QuoteAcknowledgement	b	Optional	directly on the message body
QuoteCancel	Z	Optional	directly on the message body
QuoteRequest	R	Optional	directly on the message body
QuoteStatusRequest	a	Optional	directly on the message body
SecurityDefinition	d	Optional	directly on the message body
SecurityDefinitionRequest	c	Optional	directly on the message body
SecurityStatus	f	Optional	directly on the message body
SecurityStatusRequest	e	Optional	directly on the message body

Wire format

A day number within a month, 1–31. @boarteam/fix parses the value as a number and reports parse/invalid-int when it does not lex as one; the raw string is kept either way.

Read tag 205 in TypeScript

decode.tsts

import { createFixEngine } from "@boarteam/fix";import { dictionary } from "@boarteam/fix-dict-fix42";const fix = createFixEngine(dictionary);const { message, issues } = fix.parse(raw);const field = message.fields[205];field?.name;   // "MaturityDay"field?.raw;    // the verbatim wire stringfield?.value;  // coerced to a number

Other DayOfMonth fields

314UnderlyingMaturityDay

Decode this in your own code

The same engine that produced the decoded example above is an Apache-2.0 npm package with zero runtime dependencies. It runs in Node and in the browser, and parse() returns problems as data instead of throwing.

npm i @boarteam/fix @boarteam/fix-dict-fix42

Try the decoder Source on GitHub