The calculation is deliberately simple.
Let N be repetitions, M usual effort, A assisted preparation and production, R review and repair per task, S setup, and K total upkeep for the window. All time inputs use minutes.
Usual total = N × M
Assisted total = S + K + N × (A + R)
Net time saved = N × (M - A - R) - S - K
When the per-task difference M - A - R is positive, the first repetition with no net time loss is the ceiling of (S + K) divided by that difference, with at least one repetition. Strictly positive savings start one whole repetition beyond the floor of that ratio. A result of zero is break-even, not a saving.
Both thresholds hold setup and upkeep fixed. They are not a prediction of calendar time. If more repetitions require extra maintenance, or if task difficulty changes, enter a new comparison. The calculator uses integer hundredths of minutes so exact break-even does not depend on binary decimal rounding.
What these numbers cannot tell you
Time is only one cost. Subscription fees, cognitive effort, enjoyment, privacy, reliability, and the effects on other people are not converted into a score. A workflow that fails the acceptance standard is not an equivalent replacement, even when its time result is positive.
For observations, keep comparable tasks and include failed attempts. A simple before/after comparison is not a controlled experiment and cannot isolate whether AI caused a change. Label estimates as estimates and revisit them after doing the work. Read Did the tool actually make life easier? for the broader decision.