Overhead costs of employees?

What are the common overhead costs associated with full time employees?

I've heard that if a developer's salary is $100K, he actually costs the company $150K.

I can't see where all the expenses would be that'd add another 50% to the cost.

So many things.

Obviously the salary is the largest component, plus:
You also have the cost of the recruitment process, plus any fees/kickbacks.
Depending on your local laws, tax and social security contributions.
The additional cost for someone to handle payroll.

Then you can add in the cost of benefits:
Company Car.
Gym Membership.
Health Care.
Life Assurance.
Pension.
Bonus.

and then you have the costs of covering non productive time:
Maternity/Paternity leave.
Sick leave.
Holidays.
Vacation.
Jury Service.

Assuming the employee will need some space and a des/chair and computer and heat, light, coffee, bathrooms, insurances etc, a proportion of the fixed costs should be allocated.

If you need additional software licences and training, that needs to be accounted for.

There's probably some more, but that gives you an idea of what goes into calculating the overhead part of a fully burdened employee cost.