G₁ - The first checkpoint is located at the end of the G₁ phase, just before the cell would enter the S phase. At this point, the cell will progress forward, temporarily stopping either to divide or enter the resting phase. The DNA is checked to make sure there are enough nucleotides to duplicate the DNA. The environment is also checked to make sure conditions are right for cell division.

G₂ - The second checkpoint is located at the end of the G₂ phase. If a cell passes through this checkpoint it will enter the mitotic phase. At this checkpoint, the DNA is checked again, this time for any damages that have occurred during replication. This checkpoint also ensures that all the proteins the cell needs to divide are there.

M - The last checkpoint happens during the mitotic phase, specifically at the end of metaphase. This checkpoint ensures that all the chromosomes are attached to the spindles needed to separate the chromosomes during anaphase.