I cannot be sure it is still the same, but, I was paid approximately one weeks pension, a week after my birthday, then, every 4 weeks there-after.
I was entitled to state pension at 65 (2012). My birthday is on 6th of month, I received first payment, into my bank on 12th. Thereafter, as I said, every four weeks on a Friday. My NHI letter ends "89C", if that matters.
I was used to calendar monthly payment, so, the 13 * 4 weekly payment is quite nice, it means I have one month per year, with two pension payments, so, I can buy myself new "toys"