The percentage (I assume of royalties) depends on a variety of factors, including:
- Your invention – the more likely it is to be a big money spinner and the more likely it is to succeed then you will likely get more;
- How much your base salary is. If it is already large, then you are less likely to get big percentage royalties;
- How much you need your company to make your invention happen. Your company is likely to offer less if: you are already barred from taking your invention elsewhere by your employment agreement; your company has a dominant market position; and/or if your company has to spend large sums to implement the invention;
- How unusual your skills and experience are – if your skills are unusual, and it will be difficult to get someone else to fill your shoes then you have a stronger bargaining position;
- Your employer – some employers are generous and have inventor bonuses that can be a lump sum or royalty-related. Others do not see any value in providing anything to an employee other than their salary; and
- Some industries tend to be more generous than others.
In my career, I have seen royalty rates varying from 0% to 20%, generally in the following increments: 0, 2, 5, 10, 15 and 20%. It comes down to being realistic about your bargaining position and bargaining effectively.