In clinical practice, a "month" of medication is standardised to 28 days (4 weeks) rather than a calendar month. This is consistent with NHS repeat prescribing guidelines, which recommend a 28-day interval as the optimal balance of patient convenience, clinical safety, and minimising medication waste.
As a result, your delivery date will shift by approximately 2 days per calendar month. We are unable to fix deliveries to the same date each month.