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ISODD Function

The ISODD function in Excel is used to check whether a number is odd. It returns TRUE when the number leaves a remainder of one after division by two and FALSE when it divides exactly. Decimal values are truncated toward zero before the test, so ISODD reports on the integer part of the number rather than rejecting fractional input. This function is useful for alternating logic, splitting records into two groups, and validating the parity of a count or identifier.

Key Features of ISODD:

  • Returns TRUE when the number is odd and FALSE when it is even.
  • Truncates decimals toward zero before testing, so ISODD(3.7) returns TRUE because the integer part is 3.
  • Treats 0 as even, so ISODD(0) returns FALSE.
  • Handles negative numbers by parity of the truncated value — ISODD(-5) returns TRUE.
  • Is the exact complement of ISEVEN for every value both functions accept.

Syntax:

ISODD(number)
  • number: The value you want to test for oddness. Typically a cell reference, a literal number, or a formula result.

How ISODD Works:

  1. ISODD converts the supplied value to a number.
  2. The number is truncated toward zero, discarding any fractional part.
  3. If the truncated value leaves a remainder when divided by two, ISODD returns TRUE; otherwise it returns FALSE.

Truncation happens before the parity test, not after, which is why ISODD(3.1) and ISODD(3) give the same answer.

Examples:

1. An Odd Integer:

=ISODD(7)

Result: 

TRUE

2. An Even Integer:

=ISODD(4)

Result: 

FALSE

3. Zero:

=ISODD(0)

Result: 

FALSE (zero divides exactly by two, so it is even)

4. A Decimal Value:

=ISODD(3.7)

Result: 

TRUE (3.7 is truncated to 3 before the parity test)

5. A Negative Number:

=ISODD(-5)

Result: 

TRUE

6. A Small Negative Decimal:

=ISODD(-0.9)

Result: 

FALSE (truncation toward zero gives 0, which is even)

7. Banding Alternate Rows:

=IF(ISODD(ROW()), "Shaded", "Plain")

Result: 

Alternates between "Shaded" and "Plain" down the column

8. Flagging Unpaired Records:

=IF(ISODD(COUNTA(A1:A100)), "Unpaired record present", "All paired")

Result: 

Warns when a list that should hold pairs has an odd number of entries

Notes:

  • ISODD truncates rather than rounds. ISODD(2.9) is FALSE because the integer part is 2, even though 2.9 rounds to 3.
  • ISODD is a scalar function. Unlike ISTEXT or ISBLANK, it evaluates a single value rather than mapping across a range.
  • A value that cannot be converted to a number produces an error rather than FALSE. Guard uncertain input with ISNUMBER first.
  • #N/A and infinite values are rejected as invalid numeric input.
  • ISODD is part of the IS family of information functions (ISBLANK, ISERR, ISERROR, ISEVEN, ISLOGICAL, ISNA, ISNONTEXT, ISNUMBER, ISODD, ISTEXT, etc.).

Applications:

  • Alternating Row Formatting: Combine with ROW() to band a table without a helper column.
  • Batch Assignment: Split invoices, orders, or users into two balanced groups by identifier parity.
  • Data Validation: Detect an odd count in a list where every entry should have a matching pair.
  • Scheduling: Drive fortnightly or every-other-period logic from a week or period number.
  • Checksum Logic: Implement parity checks in identifier validation routines.
  • ISEVEN: Returns TRUE if the number is even — the exact complement of ISODD.
  • ISNUMBER: Returns TRUE if the value is a number; useful as a guard before ISODD.
  • ODD: Rounds a number up to the nearest odd integer, rather than testing it.
  • MOD: Returns the remainder of a division — MOD(A1,2)=1 is the manual equivalent of ISODD(A1).
  • TYPE: Returns a numeric code indicating the data type of a value.
  • N: Converts a value to a number — logical TRUE becomes 1 and FALSE becomes 0.

Tip: ISODD and ISEVEN are exact complements, so pick whichever one makes the formula read positively rather than wrapping the other in NOT. IF(ISODD(A1), ...) is easier to scan six months later than IF(NOT(ISEVEN(A1)), ...).