Informix Error -1205: Invalid month in date.

Reasons / Common Causes

-1205 fires when a DATE value or literal's month component is invalid — per the official guidance, the month must be a one- or two-digit number from 1 to 12.

1. A DATE literal with a month value outside 1–12, per the official guidance — the direct, only cause.
2. A DATE value computed or parsed with an out-of-range month, from a malformed source string or a computation error (e.g. adding more than 12 to a month value without carrying into the year).

Solutions / Resolution

1. Correct the month to a value between 1 and 12, per the official guidance.
2. Check the source of the date value (a literal, a parsed string, or a computed expression) for where the invalid month originated.

Examples

An invalid month

INSERT INTO orders (order_id, order_date) VALUES (1, '13/01/2024');
-- -1205: month 13 is outside the valid 1-12 range

Corrected

INSERT INTO orders (order_id, order_date) VALUES (1, '01/01/2025');

Diagnostic Checks

1. Check the month component of the date value/literal for whether it falls within 1–12, and trace back to wherever it was computed or parsed if it's not a literal typo.

Related Errors / Related Topics

• -1204 — "Invalid year in date." A related date-validity error, about the year component rather than the month.
• -1206 — "Invalid day in date." A related date-validity error, about the day component rather than the month.

The date's month component fell outside 1–12 — correct it, or trace back to where it was computed/parsed.