A natural translation is “un recordatorio amable” or simply “un recordatorio” if the context already sounds polite. In everyday Spanish, “recordatorio” is the most common and flexible choice.

Good options

  • Un recordatorio amable — friendly reminder.
  • Un recordatorio cordial — a polite, warm reminder.
  • Solo un recordatorio — just a reminder.
  • Te recuerdo que... — “I’m reminding you that...,” useful in informal settings.

Example

  • Solo un recordatorio: la reunión es mañana.
  • Un recordatorio amable: tu factura vence mañana.

If you want, I can also give you formal , casual , or email-style versions.