I have heard several researchers and cattle experts discuss the recurring question of when to calve. 

Their answer for the "best" time to calve from an "efficiency" standpoint (I'll let you define those) is 30 days ahead of your "peak grass" growth time. This gets the calves born on early growth, at least after the snow.

These experts said the peak load on the from lactation cow occurs about 30 days after calving. At that point the calf is growing vigorously and needs nutriton yet is not ready to graze significantly on his own. It's all on Mama. 

In Wisconsin peak grass growth occurs about June 1 so by this logic calving should be about May 1. I have backed that up a bit and start calving about April 1 with most calves born by mid to late April.

For me "efficiency" means the least input from me. Yet I want my yearlings as big as possible when they go to the processors in late April off of corn. So it is a balancing act.  Having a tight calving period certainly helps.

Good Luck.

Jim at Dawn