How to Use Calendar Calculator
The Calendar Calculator combines two common date tasks into one tool.
- Pick the mode — Difference between dates or Add/Subtract from a date.
- Enter inputs — Two dates for difference, or a start date plus Y/M/W/D for add/subtract.
- Pick add direction — Add or Subtract.
- (Optional) Exclude weekends — Adds a business-day count or skips weekends when shifting.
- Read the result.
Formula & Theory — Calendar Calculator
Difference mode:
ymd = diffYMD(start, end)
totalDays = floor((end − start) / 86400000)
totalWeeks = floor(totalDays / 7)
totalMonths = years × 12 + months
if excludeWeekend:
businessDays = days in [start, end] where weekday ∈ Mon..Fri
Add/Subtract mode:
delta = years×Y + months×M + weeks×W + days×D
if direction == "sub": delta = −delta
target = start.add(delta)| Symbol | Meaning |
|---|---|
| start | Reference date |
| end | Target date (difference mode) |
| Y/M/W/D | Years/Months/Weeks/Days deltas |
| direction | add or sub |
The Calendar Calculator uses the same Y/M/D logic as the Age Calculator, so you can compare results across tools.
Use Cases for Calendar Calculator
- Contract expiry — Add 1 year to start date.
- Project planning — Find a date 12 weeks out.
- Travel — How many days until departure?
- Anniversaries — Difference between two notable dates.
- Pregnancy — Add 280 days to LMP for due date.
- Subscriptions — Subtract trial period to find sign-up day.
The Calendar Calculator keeps date math close at hand for everyday planning.