- What "90 days from today" actually means — return windows, payment holds and billing cycles all count the same window differently. How each desk counts, and how to protect your deadline.
- Business days: the three conventions professionals argue about — Excel counts both endpoints, payment terms start tomorrow, a third camp adds +1. Why all three are defensible.
Guides
Short, opinionated guides on the counting conventions behind the calculators.
Last updated 2026-11-04 · Calculations follow the full leap-year rule (including the year 2100 exception).