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commands/calc.md

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+---
+description: Calculate date/time differences (Claude should use date command directly)
+allowed-tools: Bash
+disable-model-invocation: true
+---
+
+# calc - Calculate date/time differences
+
+Calculate the difference between two dates or times using natural language expressions.
+
+## For Claude Code
+
+**If you are Claude**: DO NOT invoke this slash command. Use unix timestamp arithmetic via Bash tool:
+
+```bash
+date1=$(date -d "first date" +%s)
+date2=$(date -d "second date" +%s)
+diff=$((date2 - date1))
+echo "Difference: $diff seconds"
+```
+
+See the Implementation section below for the full calculation pattern.
+
+## For Users
+
+### Usage
+
+```bash
+/datetime:calc
+```
+
+The command will interactively ask for two date/time expressions, then calculate the difference.
+
+## What it does
+
+1. **Asks for first date/time**: Accepts natural language expression (e.g., "tomorrow", "2024-12-01", "next Monday")
+2. **Asks for second date/time**: Accepts natural language expression
+3. **Calculates difference**: Shows the time between the two dates in multiple units
+4. **Human-readable output**: Displays results as days, hours, minutes, and seconds
+
+The calculation uses unix timestamps internally for accuracy across timezones and DST boundaries.
+
+## Implementation
+
+**Convert dates to unix timestamps:**
+```bash
+date1_ts=$(date -d "first expression" +%s)
+date2_ts=$(date -d "second expression" +%s)
+```
+
+**Calculate difference:**
+```bash
+diff_seconds=$((date2_ts - date1_ts))
+diff_days=$((diff_seconds / 86400))
+diff_hours=$(((diff_seconds % 86400) / 3600))
+diff_minutes=$(((diff_seconds % 3600) / 60))
+diff_secs=$((diff_seconds % 60))
+```
+
+**Display result:**
+```bash
+echo "Difference: ${diff_days}d ${diff_hours}h ${diff_minutes}m ${diff_secs}s"
+echo "Total: ${diff_seconds} seconds"
+```
+
+## Examples
+
+```bash
+# Days until deadline
+/datetime:calc
+→ First date/time: today
+→ Second date/time: 2024-12-15
+→ Difference: 32d 0h 0m 0s (32 days)
+→ Total: 2764800 seconds
+
+# Time since event
+/datetime:calc
+→ First date/time: 2024-11-01
+→ Second date/time: today
+→ Difference: 12d 0h 0m 0s (12 days)
+→ Total: 1036800 seconds
+
+# Hours between meetings
+/datetime:calc
+→ First date/time: today 14:00
+→ Second date/time: tomorrow 10:30
+→ Difference: 0d 20h 30m 0s
+→ Total: 73800 seconds
+
+# Working days remaining
+/datetime:calc
+→ First date/time: today
+→ Second date/time: next Friday
+→ Difference: 2d 0h 0m 0s (2 days)
+→ Total: 172800 seconds
+```
+
+## Common calculations
+
+**Academic deadlines:**
+- "today" to "2024-12-20" - Days until assignment due
+- "today" to "next Friday 23:59" - Time to weekly submission
+
+**Project milestones:**
+- "2024-11-13" to "2024-12-01" - Sprint duration
+- "last Monday" to "today" - Week progress
+
+**Event planning:**
+- "today" to "25 Dec" - Days until event
+- "9:00" to "17:00" - Meeting duration (same day)
+
+**Time tracking:**
+- "yesterday" to "today" - Daily intervals
+- "1 week ago" to "today" - Weekly reviews
+
+## When to use
+
+- Calculate days remaining until assignment deadlines
+- Track time elapsed on projects or sprints
+- Plan event schedules and milestones
+- Verify working time between meetings
+- Calculate age or duration of events
+- Estimate remaining time for deliverables
+- Academic semester/week planning
+
+## Related commands
+
+- `/datetime:now` - Get current date/time
+- `/datetime:parse` - Parse natural language date expressions