How to use this calculator
Adding calendar days moves forward or backward by midnight-to-midnight date increments.
The method
Enter your values in the labeled fields and choose Calculate. The result panel shows the answer and supporting values when useful.
Starting date: 2026-09-15, Days to add: 45
Select Calculate to evaluate these example values.
Scope and limitations
Days must be a whole number. Business-day and holiday rules are not applied.
Common questions
Can I use different units?
Use consistent units unless this page is a unit converter. The result follows the units implied by the inputs.
Are results exact?
Displayed values may be rounded. Keep extra precision for important follow-up calculations.
Methods & verification
Formulas use standard mathematical definitions and fixed unit factors where applicable. See our methodology for numerical conventions, rounding, privacy, and limitations.