My biggest WTF on this (as a foreigner) was the late Lindsey Graham. I always knew Lindsey/Lindsay as a female name.
Either way, peeking through the list, seems to me names which end with a vowel are usually feminine. However, there's a caveat: names end up shortened, and over time even those get shortened.
'Brit', 'Britney' for 'Brittany'.
'Gerry' or 'Geri' or 'Ger' for 'Gareth' (Dutch variant: 'Gerrit'),
'Pat', 'Patty' for 'Patrick', 'Patricia'.
'Pen', 'Penny' for 'Penelope'
'Ash' for 'Ashley'.
'Tash' or 'Tasha' for 'Natasha', 'Nata(s)cha' (a variant of Nathan/Nathaniel?)
'Toni', 'Tony', or 'Ton' for 'Antonia', 'Anton', or 'Antonius'.
Skimming through the quick examples I came up with, one thing stands out: if it ends with an 'a', feminine. I believe this stems from Latin? It also appears Brittany is a very British example, whereas say 'Tony' stems from a Catholic background. People with that background get very traditional names, but they're always practically shortened. Annoyingly, you'd have to mention your complete name on say a form, but otherwise you get a wider choice since you have like three names, and they're relatively long so more variety to pick from.
Either way, peeking through the list, seems to me names which end with a vowel are usually feminine. However, there's a caveat: names end up shortened, and over time even those get shortened.
'Brit', 'Britney' for 'Brittany'.
'Gerry' or 'Geri' or 'Ger' for 'Gareth' (Dutch variant: 'Gerrit'),
'Pat', 'Patty' for 'Patrick', 'Patricia'.
'Pen', 'Penny' for 'Penelope'
'Ash' for 'Ashley'.
'Tash' or 'Tasha' for 'Natasha', 'Nata(s)cha' (a variant of Nathan/Nathaniel?)
'Toni', 'Tony', or 'Ton' for 'Antonia', 'Anton', or 'Antonius'.
Skimming through the quick examples I came up with, one thing stands out: if it ends with an 'a', feminine. I believe this stems from Latin? It also appears Brittany is a very British example, whereas say 'Tony' stems from a Catholic background. People with that background get very traditional names, but they're always practically shortened. Annoyingly, you'd have to mention your complete name on say a form, but otherwise you get a wider choice since you have like three names, and they're relatively long so more variety to pick from.