Add or subtract days from a date
Find the calendar date before or after a starting date.
Your inputs
Your results
Ready when you areYour results will appear here.
How it works
Add a signed whole-day offset to a validated UTC calendar date and format the resulting date without local timezone or daylight-saving shifts.
Read the source reference ↗A few things to know
Calendar days only. Does not adjust weekends, holidays or business deadlines. Results must remain within four-digit years; month arithmetic is not modeled.
When to use this tool
Move a date forward or backward by a precise number of calendar days. Month boundaries are crossed naturally rather than treated as equal-length months.
- Find a follow-up date.
- Subtract a preparation interval.
- Cross a month boundary.
How to use add or subtract days from a date
Prepare the inputs
Enter the quantities and units used by your source.
Choose the settings
Choose the assumptions and compare them with your actual situation.
Review and export
Review the result, then download the calculation report.
Try the supplied example
Inputs
start: 2026-01-31; days: 30
Result
Thirty days after January 31, 2026 is March 2, 2026.
What it means
Use a negative offset to subtract days; check nonworking-day rules separately.
Common mistakes to avoid
Thirty days is not always a month
Thirty days is not always a month.
Check working-day deadline adjustments separately
Check working-day deadline adjustments separately.
Frequently asked questions
Definitions, edge cases, and practical next steps for this tool. Search all tool FAQs ↗
How do I subtract days?
Enter a negative whole-number offset.
Are weekends skipped?
No. All calendar days count.
Does adding 30 days mean one month?
No. Calendar months have different lengths.
Are leap days handled?
Yes. UTC calendar arithmetic includes them.
Does timezone change the answer?
No. Inputs are treated as dates at UTC midnight.
Can I enter fractional days?
No. This tool requires whole-day offsets.
Are my inputs uploaded or stored?
Processing happens locally in your browser. This tool does not upload inputs. Downloads stay on your device; sharing or opening them in another service is your choice.
What should I check before using the output?
Calendar days only. Does not adjust weekends, holidays or business deadlines. Results must remain within four-digit years; month arithmetic is not modeled.
Explore the topic in the blog
Sources and method
Use the references below to check definitions and platform guidance. The model’s scope and limits are explained above. Read our editorial standards.