How long is a Sim year?

Each season is set at 28 days, which is equal to a month in my mind, and I play each season 3 times before moving on to the next one. 4 seasons times three playthroughs equals one Sim year. I also play with aging off and age up my Sims when I feel it's the right time. I play rotationally through many families and single Sims, and when there are as many things to do as there are now in the game, I like to take my time with every Sim so they can experience everything without me feeling pressured to move through the game too quickly. That, plus I get very attached to my Sims and their stories and want them around for as long as possible.