Employed at 100k Euro, no kids, not married:
- 27.406 Euro income tax
- 1.243 Euro solidarity tax
- 7.923 Euro pension fund
- 1.022 Euro unemployment insurance
- 1.030 Euro statutory nursing care insurance
- 4.440 Euro health insurance
= 56.932 Euros left over.
Health care can be made a bit cheaper with a private insurance company but this is the ballpark most people would be in. All the listed taxes and insurances are mandatory.
Freelance with 100k Euro, no kids, not married:
- 22.290 Euro income tax
- 1.225 Euro solidarity tax
- 10.594 Euro health insurance
- 15.840 Euro pension fund
= 51.310 Euro
However: Paying into the pension fund is not mandatory as a freelancer and you can also choose how much to pay and health insurance can be made cheaper here as well. Health insurance and pension fund will be deducted from your taxable income. Also as others have mentioned you can suddenly deduct a lot of things (phone bills, parts of your electricity bill, buying a new laptop etc.).
The main kicker here however is this: I work as a freelance webdev and so far I have managed to make about 80 Euros/hour which given my current workload will result in about 130k Euros of income this year. I have yet to get an offer from any company willing to pay more than 100k.