Exact model

Two UUIDv4 values collide

Probability:
1.88 × 10⁻³⁵%
Odds:
1 to (5.32 × 10³⁶)
dBan
−367.3 dBan

Generate two UUIDv4 values independently and seeing this particular pair come out identical would be an extraordinary coincidence.

Calculation

p = 1 / 2¹²² = 1 / 5,316,911,983,139,663,491,615,228,241,121,378,304

Assumptions

Both UUIDv4 values use independent, uniform 122-bit random fields from a reliable generator. The model covers one pair. In a large collection, the birthday effect counts many possible pairs and raises the probability of at least one collision.

Sources

  1. IETF RFC 9562: UUID version 4 published May 2024; checked 27 October 2026