Treats are part of the daily total
A complete dog food is formulated to provide balanced nutrition when fed in the recommended amount. Everything else you add — biscuits, chews, table scraps, training rewards — sits on top of that.
A commonly repeated guideline among vets and nutritionists is that treats should make up only a small share of daily calories, with the rest coming from a complete diet. The exact share and the exact number of biscuits depend on your dog.
Size changes everything
A 4 kg dog and a 40 kg dog have very different calorie needs, so the same biscuit is a very different proportion of their day. Small dogs gain weight from extras far more easily than owners expect.
If you use food for training, the simplest approach is to use tiny pieces and count them, rather than switching to a lower-value reward.
Questions worth asking your vet
How many treat calories a day suit my dog's current weight and body condition?
Should I reduce meal portions if I train with food regularly?
Are there foods I should avoid entirely because of my dog's health history?