Written for Mexico. This analysis applies to Mexican federal tax law — ISR (income tax), IVA (VAT) and SAT rules — and cites Mexican statutes. Amounts are in Mexican pesos (MXN).
Every Mexican employer lives with two acronyms nobody ever formally introduced: SUA and SIPARE. The standard confusion — thinking they're the same thing, or that one replaces the other — produces misapplied payments, avoidable surcharges and nasty surprises with Infonavit (the national housing fund). The reality is simple: SUA calculates, SIPARE collects. Here is the full map of the social-security payment cycle, with the official links in the Resource Center.
SUA: the system where the employer self-determines
The Sistema Único de Autodeterminación (SUA, the single self-determination system) is the software (from the IMSS, free, desktop) where the employer calculates its three families of obligations: IMSS employer-employee contributions, Infonavit contributions and loan amortizations, and RCV (retiro, cesantía y vejez — retirement, severance-at-old-age and old-age). It's fed with your roster of workers, their base contribution salaries (SBC), movements (enrollments, terminations, salary changes, incidents) and your work-risk premium — and it produces the exact calculation for each period. It's mandatory from 5 workers up; with fewer, you can use the pre-filled statement the IMSS sends you (EMA/EBA — the monthly and bimonthly determination summaries) or SUA itself. Golden rule: the IMSS proposal is exactly that — a proposal, built from what the institute knows; if your movements for the month aren't reflected in it (that termination from last week), paying it without reviewing means paying too much or too little, and both cost you.
SIPARE: where you generate the payment reference and pay
The Sistema de Pago Referenciado (SIPARE, the referenced-payment system) is the portal where that calculation becomes a línea de captura (payment reference) payable through online banking or at a teller window. You upload the payment file that SUA generates (or use the proposal), get the reference and pay — referenced payment ties your money exactly to the obligations it covers, which is what eliminates the "unidentified payments" that historically poisoned employer accounts.
The calendar that shows no mercy
IMSS contributions are paid monthly, no later than the 17th of the following month. RCV and Infonavit are paid bimonthly — no later than the 17th of the month following the two-month period (January–February is paid by March 17, and so on). The cost of failing is threefold: automatic inflation adjustment and late-payment surcharges, the loss of subsidies/benefits where applicable, and — the one that hurts most — the exposure of your workers: a delinquent employer is liable for benefits the IMSS denies for lack of payment, and a negative social-security compliance opinion (opinión de cumplimiento) closes doors with corporate and government clients today just like the SAT one does. The amount of all this — how much it is, who contributes it, on what base — is broken down in our guide to employer-employee contributions and is estimated instantly with our employee-cost calculator.
Is your SUA-SIPARE cycle on reliable autopilot — or on "someone's always done it"?
Reviewing the full cycle takes one session: enrollment movements up to date, SBC correctly integrated, work-risk premium current, bimonthly variability correctly calculated, and reconciliation against the IMSS issuances. The typical findings — poorly integrated salaries, outdated premiums, silent differences piling up surcharges — are corrected cheaply today and at ruinous cost in an on-site IMSS inspection.
Frequently asked questions
What exactly is the 'variability' adjustment done each two-month period?
Workers with variable income (commissions, piecework, recurring overtime) recompute their base contribution salary each two-month period using the average of the variable portion from the prior period — the 'variability modification' filed in the first business days of each period. Skipping it is one of the most common causes of discrepancies in IMSS inspections.
I paid using the IMSS proposal and then noticed a termination was missing — what do I do?
File the movement and adjust: the system will offset/credit the difference in the next issuance, or request a refund/offset of the overpaid amount. What matters is that enrollment movements are filed within their deadlines (5 business days) — the real cost wasn't the overpayment, it was the habit of paying proposals without reconciling.
Can SIPARE be used to pay old debts or installment agreements (convenios)?
Yes — it also generates payment references for IMSS tax credits, differences and authorized installment plans. If you carry debt, the right combination is usually: size it precisely (don't pay 'whatever the system says' without reviewing the determination), correct what is proper and settle the rest — IMSS credits are litigated and negotiated just like SAT ones.
Let's talk about your case
The first step is always the same: an honest diagnostic of where you stand. Write to us on WhatsApp or call — a reply the same business day.