Literacy of negotiating personal compensation for work is one of the most important skills in a career. The labor market functions on the principle of supply and demand: your knowledge is "goods", and the employer is the buyer.
The employer actually doesn't care about your net, but the "total cost" (Gross 2). The amount that lands in your account depends on your private factors (children, deductions) over which the employer has no influence. Negotiate based on the gross base, which is fixed and the same for everyone.
"I want a raise because I've been working here for a long time and the rent has gone up."
"I increased the department's productivity by 15% and directly contributed to the growth of company revenue. I believe an increase in gross salary is justified."
Research average gross salaries for your position and experience level on statistical portals or forums. Come to the negotiation with specific numbers.
If the budget for gross salaries is limited, negotiate for tax-free allowances such as meal allowance, transportation, bonuses, or education. This costs the employer less and directly increases your net income.