Converting a net salary (the amount an employee receives in their account) back into a gross salary ("Gross 1") is a more complex process. Since taxes and contributions are calculated on the gross amount, calculating net to gross requires solving a reverse mathematical operation.
When calculating from gross to net, steps and percentages are applied linearly. However, when starting from the net amount:
The calculation is usually solved by setting up an equation where "Gross" is the unknown (X). Computer programs (calculators) set up an equation based on a known net amount, personal deduction factors, and location, and through algebraic manipulations "extract" X (Gross amount).
This approach requires the program to pre-check which tax bracket the requested gross amount falls into based on the estimated net amount.
Many computer systems simplify this problem using the so-called iterative approach or a brute-force method of close guessing.
When you negotiate a salary by talking about a net amount, the employer always has the so-called Gross 2 in mind. Even though you are negotiating about the money you will receive, the actual cost for the company specifically for your position will be significantly higher due to contributions paid on the salary, i.e., on top of your agreed Gross 1 amount.