1. What the "PDT 621" is (and what it no longer is)
For years, filing the monthly IGV and Renta pago a cuenta meant installing the Programa de Declaración Telemática (PDT) on your computer and filling out form 621 there. That's no longer necessary today: SUNAT migrated that filing to the Formulario Virtual N.º 621 — IGV Renta Mensual, which you fill out directly from SUNAT Operaciones en Línea, with nothing to install. A lot of people still call it "PDT 621" out of habit, but technically it's now a web form.
Whatever name you use for it, it's the filing that almost every business in Peru submits each month (with the exception of NRUS, which files differently — see our article on tax regimes).
2. The schedule based on the last digit of your RUC
Each year SUNAT publishes a filing schedule with different dates depending on the last digit of your RUC — not everyone files on the same day of the month. Taxpayers qualified as Buenos Contribuyentes also get an extra day beyond the general schedule.
Filing late doesn't just trigger a fine: if there's tax owed, late-payment interest also accrues starting the day after the due date, not from the day you actually file.
3. The boxes that cause the most confusion
- Taxed vs. exempt sales: not every sale is subject to IGV — mixing up these two boxes distorts the month's débito fiscal.
- Purchases tied to taxed sales: crédito fiscal can only be taken on purchases linked to taxed transactions, not on any expense.
- Retenciones and percepciones suffered: these go in boxes separate from the "regular" crédito fiscal — mixing them up throws off the balance due.
- Saldo a favor from the prior period: it has to be carried forward exactly, month after month — a mistake here carries forward indefinitely until someone catches it.
4. IGV: debit, credit, and the saldo a favor
The IGV you pay each month is, in essence, the difference between your débito fiscal (the IGV you charged on your sales) and your crédito fiscal (the IGV you paid on purchases linked to those sales). If the credit exceeds the debit, there's nothing to pay that month — a saldo a favor is generated and carried to the following period, and so on until it's used up against future debits (except for special mechanisms, like the exporter's saldo a favor, which can actually be requested as a refund).
5. Renta: the month's pago a cuenta
The same form also declares the monthly pago a cuenta of the Impuesto a la Renta de Tercera Categoría — a prepayment toward the annual tax, not the final tax. How that prepayment is calculated (coeficiente, 1.5%, or 1% if you're under RMT below a certain cap) depends on your regime and your track record; we cover it in detail in this other article.
6. Common filing mistakes
- Declaring sales that don't match what you've already issued as an electronic receipt — SUNAT already has that information independently, and the mismatch shows up as a visible inconsistency.
- Taking crédito fiscal on purchases without the receipt to support it, or on purchases unrelated to the business.
- Carrying the saldo a favor forward incorrectly from one month to the next.
- Filing late because you didn't have your RUC digit's schedule on hand.
7. How factsimil handles it
Since factsimil already knows which receipts you issued and their status with SUNAT, the Financial Reports module builds the period's taxed/exempt sales detail directly from your actual receipts — not from a separate copy that can drift out of sync. If you also keep your purchase register, the crédito fiscal comes from the same place.
You can review the full accounting detail in Contable, the plan that includes PLE, SIRE, and financial reports.