When to start using a belt is a topic that is regularly misunderstood and commonly mistimed. The fact is, you really don’t ever NEED a lifting belt. Most lifters start using a belt to protect their back and avoid injury. What most lifters don’t realize is that by using a belt for solely that reason typically means you are relying on the belt to overcome and compensate for poor technique. As long as you are bracing properly and using sound technique, you really shouldn’t have any back issues as a result of any particular movement.
A belt becomes useful when you are trying to overload on certain movements, such as the squat and deadlift. Overloading simply means, trying to add more weight to the bar week by weight in order to improve overall strength and hypertrophy. Again, the belt should not be a substitute for poor technique. The belt should be used as an assistive tool so that you can brace yourself even harder by contracting your core against the belt creating more intra abdominal pressure.
So let’s go back to the question at hand, when do you NEED to start using a lifting belt? I think the right time varies per individual. I would recommend staying beltless until you reach a point when your form and technique are dialed in. At that point, you may want to invest in a lifting belt so that you can add more weight to the bar and break past any current plateau. Start thinking of the belt as a tool for progression, not as a substitute for poor technique.