There is unfortunately no clear-cut answer to this question because it is highly variable. It depends on a number of factors including industry, value proposition, and target demographic, amongst others. A fair rule of thumb is plan to spend $300 in the first month and then revise your budget each week as you learn what the cost per result looks like. Then, you can switch your budget depending upon available funds, campaign costs, and your goals.
There are two things that are very important to remember when calculating your digital advertising budget.
The first is that your digital advertising budget must be calculated in the context of your overall marketing budget.
Secondly, it’s a marathon not a sprint. This means that you don’t want to spend your entire annual digital advertising budget in one week. Why? You don’t want to spend your entire budget at once because the value of each dollar you spend increases with campaign optimization. You want your money to produce the best results possible so by spreading spend out over time you will see that efficiency increases with the learnings you benefit from with each new campaign iteration. Another way to think about this is that you don’t want stakeholders to see rapid growth in month one and then no growth in months 2+.