The gross salary is not what the employee receives
The first concept that must be internalized is the difference between gross salary and net salary. The gross is what you agree with the employee; The net amount is what actually falls into your account after subtracting the legal withholdings. In the middle are the ISR and the IMSS contributions that correspond to the worker.
And there is a second number that takes many owners by surprise: the total cost to the employer. In addition to the salary, you as an employer pay your part of the contributions to the IMSS, Infonavit and SAR, plus the legal benefits. That is why it is said that an employee costs more than his salary: the real cost is usually between 20% and 35% above the gross, depending on the salary level and the benefits you offer.
Understanding these three numbers—gross, net, and employer cost—is what allows you to budget well and avoid surprises when it comes time to pay fees.
The IMSS: what it is and who pays what
The Mexican Social Security Institute gives your employees medical care, disabilities, daycare and the basis for their pension. Registering your workers with the IMSS is not optional: it is a legal obligation from day one, and failure to do so exposes the business to heavy fines and lawsuits.
IMSS contributions are calculated based on the Base Contribution Salary (SBC), which includes the salary plus certain benefits. This cost is distributed: you retain a part from the worker's salary, and another part—the largest—is paid by you as the employer. Every month and every two months you must pay (pay) these fees to the IMSS and Infonavit.
The payroll ISR: the withholding you make for your employee
The ISR (Income Tax) on salaries works by withholding: you, as the employer, calculate how much ISR the employee must pay according to the table, deduct it from their salary and deliver it to the SAT on their behalf. The employee does not carry out this procedure; you are the obligatory intermediary.
The calculation uses the SAT tables and rates, which are progressive: whoever earns more retains a higher percentage. There is also an employment subsidy in certain salary ranges, which reduces the retention of lower-income workers. Doing this calculation by hand every fortnight for multiple employees is where most errors creep in.
- You withhold the ISR according to the current SAT table for the period (weekly, biweekly or monthly).
- You apply the employment subsidy when applicable.
- You pay (pay) the withheld amount to the SAT within the established deadlines.
- At the end of the year you do the annual calculation to adjust differences.
The CFDI payroll receipt: mandatory in each payment
Every time you pay an employee, you must issue a stamped payroll receipt, which is a CFDI with payroll supplement. It is not an informal paper: it is a tax receipt that details perceptions (salary, bonuses, overtime), deductions (ISR, IMSS, loans) and the net paid.
This receipt is your support to deduct the expense from salaries, and is the worker's proof before the SAT and for procedures such as credits. Issuing it incorrectly or not issuing it costs you the deduction and exposes you to sanctions. Since the payroll CFDI is fed into the calculation, any errors in the calculation are carried forward to the receipt.
Automate payroll with Aura
Payroll is probably the process where it is best to stop calculating by hand, because it combines changing rules (ISR tables, SBC, subsidies) with the obligation to stamp each receipt. An error is multiplied for each employee and for each period.
Aura's payroll module automatically calculates the ISR according to the current tables, the IMSS quotas on the Base Contribution Salary, and the legal benefits, to then generate and stamp the CFDI receipt for each employee in each period. You define the salaries and incidents of the period (absences, overtime, bonuses), and the system does the rest: calculation, receipt and accounting record, all in one place.
Since payroll lives within the same platform as your accounting, salary expenses are automatically recorded and classified, and cash flow already considers the entire employer cost. Paying payroll stops being a risky operation every fortnight and becomes a reliable process that you complete in minutes.
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Start your trial →Frequently asked questions
Am I required to register my employee with the IMSS from the first day?
Yes. The law requires the worker to be registered with the IMSS from the moment the employment relationship begins. Failure to do so exposes the business to fines, retroactive payment of fees with surcharges, and legal risks if the employee suffers an accident. It is not optional or negotiable.
How much does an employee really cost me in addition to their salary?
As a general rule, between 20% and 35% additional to the gross salary, depending on the salary level and benefits. This percentage covers your part of IMSS, Infonavit, SAR fees and legal benefits such as bonuses, vacations and vacation bonuses. It is advisable to budget for it before hiring.
What happens if I don't stamp the payroll receipt?
You cannot deduct the expense from that salary and you are exposed to SAT sanctions. The CFDI payroll receipt is mandatory in each payment; It is the tax receipt for both you and the worker. An automatically ringing system eliminates the risk of forgetting it.
Is the payroll ISR paid by the employee or by me?
The ISR belongs to the employee, but you have the obligation to withhold it from their salary and report it to the SAT on their behalf. You function as an intermediary: if you do not withhold or pay what was withheld, the responsibility and penalty fall on you as the employer.