First some background, I've worked for a consulting company like yours, where I was hired out for around 5 times my take home pay, I now work as a lone software consultant contractor and charge my own rate.
Firstly, it may feel like your employer is just raking in profit from the work you are doing. While they will be making a profit over what they are paying you, consider the service they are offering to both you and the company that you've been hired out to (I'm guessing at a few of these and the list may not be exhaustive, but it illustrates my point):
Services to you:
You are an employee, and have all of the security and benefits that the law dictates an employee should have.
Your company may have invested time in training you so that you are more able to complete the task required by the hiring company.
You are guaranteed work while you are employed by your employer, your employer is not guaranteed anyone's business.
Out of the whole time you've been employed, how many of your hours have been chargeable?
Your company manages your payroll, pays you holiday and sick time. All of this you would have to provision your self if you went it alone.
Services to the hiring company:
- Provision of skills without the need for hiring company to recruit
- Management of personnel services such as payroll
- Guarantee of a replacement for you if you leave your company / are off sick / on holiday
- Provision of specialist skills without training
So, are you getting a fair cut?
If you have been subcontracted out, you maybe in a powerful position in terms of renegotiating your salary. If the hiring company likes you, and your employer has enough margin in the rate they charge for you, they may well be willing to part with some of the profit they are making on your time. How much depends on the numbers and your negotiating skills.
Bear in mind that your employer has many overheads and taxes to pay, and the Gross profit they make on your time, will not be the same as the Net profit.
Also, if you manage to negotiate a pay rise, if the contract with the hiring company ends, and your company cannot immediately find more chargeable work for you, you may be too expensive to keep on the books, and be made redundant. Depending on how specialist your skills are, this could be a good / bad thing. If the skills are pretty niche, you'll need to be extra careful not to upset people.
That didn't really answer your question?
There is no definite answer. Back to my background, I left my employer while contracted out to a hiring company. I was fed up with the travel mostly. The hiring company offered me work, suggesting they could work around any contractual obligations to my employer, but I turned it down.
I now freelance / contract in the same industry. Do I earn 5 times my old salary? Nope. It's pretty good, but not that good! Companies can often charge more than you could as an individual contractor, for reasons including the services to both parties above. Plus I have accounts to do and no job security. Not everyone is comfortable with this style of work.
All of that said, don't sell your self short. I've been happier in my work since going alone, and you might be too.