Method & assumptions
How Date Duration Calculator derives its result.
Formula
Elapsed days = difference between the two dates at midnight UTC. Month count is a completed-calendar-month estimate.
Recommended workflow
- Choose start and end dates.
- A negative count means the end date precedes the start date.
- Confirm inclusive/exclusive and holiday counting rules for deadlines.
Limitations
Legal, billing, and contract deadlines can use special counting rules. Do not rely on this for a legal deadline.
For important work, verify assumptions against the authoritative source for your task.