Different questions
A vulnerability assessment answers: what known weaknesses exist across this estate? It favours breadth, repeatability and automation.
A penetration test answers: what can an attacker actually achieve here? It favours depth, chaining and human judgement.
Different output
A vulnerability assessment produces a prioritised inventory of findings. A penetration test produces demonstrated impact — this specific route led to this specific access.
The distinction matters for decision-making. An inventory of medium-severity findings is difficult to prioritise. A demonstrated route to your customer database is not.
Different frequency
Vulnerability assessment is a recurring hygiene activity and should run continuously or on a short cycle.
Penetration testing is periodic and event-driven: annually, before a major release, after significant infrastructure change, or when a customer requires independent validation.
You need both, for different reasons
Vulnerability management keeps the volume of exploitable weaknesses low. Penetration testing establishes whether the ones that remain — combined with configuration and design decisions — add up to a viable attack path.
Buying one and describing it as the other is the most common way organisations end up with less assurance than they believe they have.