Calculate the number of days between two dates

ServiceNow's date arithmetic is deceptively tricky because GlideDateTime objects store timezone-aware timestamps while most developers think in calendar days. The naive approach of subtracting getNumericValue() results can give you 0 days when you expect 1 because you're working with millisecond precision across timezone boundaries. GlideDuration.subtract() handles the timezone math correctly and returns a duration object that converts cleanly to whole days.

When to use this

• When calculating SLA elapsed time in business rules or scheduled jobs
• When building aging reports that need accurate day counts across date ranges
• When processing incident or change records that span multiple timezone changes
• When you need both calendar days and business days for the same date pairs

When NOT to use this

• Don't use this in client scripts — use GlideAjax to call server-side date calculation
• Don't use this for same-day time differences — use GlideDuration methods for hours and minutes
• Don't use this in loops over thousands of records — pre-calculate and store the values
• Don't use manual millisecond arithmetic — it fails across daylight saving boundaries

Key behaviors and gotchas

• getDurationValue() returns milliseconds — always divide by 86,400,000 for days
• Math.floor() prevents 0.99 days from rounding up to 1 day
• Business day calculation requires a valid schedule sys_id — invalid schedules return 0
• GlideDuration.subtract() parameter order matters — end date first, start date second
• Negative durations occur when start date is after end date — handle explicitly or use Math.abs()
• Invalid date strings pass the truthy check but fail isValid() — always validate before arithmetic