D-day Calculator
Days Until or Since
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Add or Subtract Dates
Add or subtract calendar days, months or years with negative offsets and month-end handling.
Processed on your device · No file uploads
Your selected files and results are processed on this device. They are not sent to external servers or stored on our servers.
How processing works- 01Select input
- 02Process locally
- 03Review & save
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Example input & result
Input & settings
2024-01-31 + 1 month
Expected result
2024-02-29
Missing dates clamp to month-end. A calendar month is not a fixed 30 days.
How to use Add or Subtract Dates
- 01Choose input values or files.
- 02Check settings and select Calculate or Run.
- 03Review the result and limitations, then save if needed.
Frequently asked questions
Are inputs stored on a server?
No. Inputs and results are processed on-device without uploading or storing them with the operator.
What does this tool do?
Add or subtract calendar days, months or years with negative offsets and month-end handling.
What is an example result?
2024-01-31 + 1 month → 2024-02-29
What are the limits and assumptions?
Missing dates clamp to month-end. A calendar month is not a fixed 30 days.
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