Compare the purchase price and variable cost of two candidates over the same period. The labels describe an inkjet or tank candidate and a laser candidate; the formula can also compare two supply systems. All numbers are user assumptions.
Formula and example
Total = purchase price + monthly sides × months × variable cost per side. Crossing volume = (inkjet purchase − laser purchase) ÷ (laser CPP − inkjet CPP). Hypothetical $350 at $0.008 and $200 at $0.025 produce totals of $407.60 and $380 at 7,200 sides. Their lines cross near 8,824 sides; at 200 sides/month, roughly 44 months.
Interpret the crossing correctly
A nonnegative crossing is the volume where the modeled costs match. Equal running costs have no finite crossing unless the purchase prices also match. A negative crossing lies outside a normal nonnegative printing scenario. The tool reports the two totals even when there is no usable crossing.
Use the same included cost layers in both CPP inputs. Add paper and periodic parts consistently if you want them included. Excluded costs and uncertain maintenance can change the result. More importantly, price arithmetic cannot certify photo quality, paper support, scanner workflows, OS support or idle reliability. A candidate must pass your task requirements before its cost matters.