How much should I spend on marketing?

As a rough frame, 5-15% of annual revenue. A young company still building recognition needs the top of that range or more; an established business with repeat customers can sit at the bottom. Margin decides a lot: the higher your margin, the more you can afford to pay for a customer.

Treat the range as a starting point, not a rule. It goes up with low awareness, strong competition and long buying cycles. It goes down with high repeat purchase rates, strong word of mouth and categories where people search on their own. The worst option is a budget that changes every month on instinct - marketing needs stability or you can't tell what worked.