It's not quite as cold here. The ride home last night was about -6C.

I've found three things matter a lot when cycling in winter.

First is that the outermost layer needs to be windproof. Otherwise the wind--either from Mom Nature or my own motion--just blows the heat away. My cycling jackets and my winter tights are both wind and water resistant.

Second is that sweat management is even more important in winter. Wearing too much means sweating through my layers. Wet clothes = hypothermia. So I tend to underdress just a bit, and compensate by pedaling harder.

My rule of thumb is that when I first step outside, I should feel like I need to turn around for another layer. Experience has shown that starting out like that means that by 10-15 minutes into the ride, I'm unzipping things, which is just about right for me. The coldest it's gotten here since I started cycling to work is about -20C. I still had the pit zips open on my jacket to let the moisture out.

Third is that how hard you ride makes a big difference. I ride hard and so generate more heat. Yesterday at -6C, I wore one long-sleeve wicking t-shirt and my jacket. Somewhere between there and -17C, I'll add a second long-sleeve wicking t-shirt. Guys who go along nice, slow, and easy don't make as much heat, and need to dress a bit heavier. Because of this there is no one-size-fits-all recommendation.

EDIT: Riding around slightly underdressed for conditions means I'm significantly underdressed if I have to stop for more than a couple of minutes, like if I get a flat or other mechanical. I generally carry a couple of extra layers with me just in case that happens. I can't wear them for just in case because I'll soak them through.