Extended Payment Code
What it is
Number of months for extended/installment payment.
DE 67 on the wire
Bitmap position
DE 67 is bit 3 of the secondary bitmap: byte 1, mask 0x20. A secondary bitmap with only DE 67 present reads 2000000000000000 in hex. The secondary bitmap is only sent when bit 1 of the primary bitmap is set, so any message carrying DE 67 has a primary bitmap whose first hex digit is 8 or higher.
Length
DE 67 is fixed length: always 2 digits, with no length prefix. A parser reads exactly that many and moves on, so shorter values are right-aligned and padded with leading zeros.
Size in the message
At most 2 bytes when the message travels as text (ASCII or EBCDIC), or 1 bytes in binary dialects that pack digits as BCD.
Format n
Format n means numeric: the digits 0–9 only.
Specification reference
Defined in ISO 8583:1987 (base). Card networks publish their own dialect tables (Visa BASE I / V.I.P., Mastercard CIS) that refine formats, lengths, and — for private-use elements — the entire layout. Always confirm against the interface specification you implement.