When does the luteal phase end?

I’m trying to work out if I have a short luteal phase. I’m 12dpo and started spotting. My period is due on the 19th and I always start spotting 1-2 days before af so this is normal for me. But does the luteal phase end when I start spotting, or when I start full flow? If it ends when I start full flow my luteal phase would go to 13 days, but if it ends when I start spotting it would be only 11..