Context specifics will always drive a more accurate answer. Much depends on the valuation and other variables, which this question asks to put aside.
The general rule of thumb is:
For seed rounds, expect anywhere from 10% to 25% as a normal range.
For Series A, expect 25% to 50% on average.
For Series B, expect roughly 33%.
As you advance to the next funding round, you should realistically expect further dilution. Founders start with 100% ownership. Seed rounds – the earliest stage of funding, usually from family and angel investors – typically dilute founders’ ownership by an average of 15%.
By the time you reach the Series A stage, you need to be prepared for further dilution. Series A investors are usually funders who provide venture capital for emerging companies. Since their funding typically exceeds $2 million, their percentage of ownership can be as high as 50%.
If you get to the Series B round, expect a dramatically different mindset from earlier funders. Whereas Series A and seed investors believe in your vision and have bought into the prospects of your company, those in Series B want to see that you’ve successfully progressed and satisfied important milestones. They typically see about 33% ownership, which will dilute all previous ownership percentages.
You also need to reserve a percentage for the option pool – usually, about 10% to 15%.