Which checkpoint of the cell cycle is considered the "point of no return"?

The G1 checkpoint at the G1/S transition is referred to as the “point of no return”. Once the cell passes this checkpoint, it becomes irreversibly committed to completing the cell cycle to divide into two daughter cells. After this point, extracellular signals are no longer necessary to generate proliferation. External cues such growth factors play a significant role in carrying the cell past the G1 checkpoint. Cell size, adequate amounts of nutrients, and genomic DNA are all checked for at the G1 checkpoint. A cell that is unable to meet all the requirements will not be permitted by the cell to progress into the S phase. At that point, the cell may put a stop to the cycle, attempt to repair it, or may enter the G0 phase.