

GDP is basically a measure of how much work is getting done. So, if you save your money, you’re not contributing to it. The moment you spend some, that spent money goes into the calculation.
Whether this constitutes any kind of real “growth” or not in your economy is a different topic. There are already debates on how useful GDP is as a useable measurement.
Nothing wrong with it as a method, so long as it makes some predictions we can then test for.