Decide what the top set means
Before lowering the weight, decide what the top set was supposed to prove. Was it a strength exposure, a technique check, or the heaviest work before volume?
If the top set moved as expected, the back-off work can usually stay close to the plan. If it was slower or messier than expected, the back-off load should give you more room.
Example: after a heavy set of 3 at 150 kg, a 10% drop gives 135 kg. That can be a useful starting point, but the set quality decides whether it is still right.
Choose the drop from the goal
A smaller drop keeps the work closer to the top set. A larger drop gives more room for cleaner reps, shorter rest, or extra volume.
Do not treat the drop as a universal rule. The right reduction depends on the lift, reps, fatigue, rest periods, and how close the top set was to failure.
Use a conservative first drop when the top set was a near max, a high-RPE set, or a lift that creates more fatigue for you.
Make the back-off sets loadable
After choosing the reduction, round the target to the plates or dumbbells available. A clean, repeatable load is more useful than a perfect spreadsheet number.
Use volume load only to compare similar back-off work, because the arithmetic cannot see technique, bar speed, rest, or how hard the sets felt.
Log the reason, not just the number
Record the top set, the back-off load, and why you chose it. After a few weeks, those notes reveal whether a 5%, 10%, or 15% drop tends to match the training goal.
Use Protocol to run the block and keep those session decisions attached to the routine instead of scattered across calculator tabs.