Blossom end rot

Blossom end rot

We kind of came late to the tomato game this year, but bought a patio type plant and two roma plants for our balcony. After initially being worried they wouldn't pollonate, I discovered there were tomatoes growing. Then a few days ago I found the largest one on the patio had what I assume is blossom end rot. And now I see the 3 smallish roma ones growing do too. They were planted in new potting soil, and are outside so have been getting regular rain and watered when we've had a dry spell. I read somewhere it can be a calcium deficiency, is that correct? Best way to correct it for future fruit or is it too late now?
Plumerias; Shiitake Mushrooms

Plumerias; Shiitake Mushrooms

My Bog Garden

My Bog Garden

Calandiva

Calandiva

Plant ID por favor

Plant ID por favor

before photos of tricycle

before photos of tricycle

the beginning starts here…

the beginning starts here…