Simple Date Calculator for Planning & Deadlines

Date Calculator: Quickly Add or Subtract Days

What it is: A simple tool that lets you add or subtract a specific number of days to/from a given date and returns the resulting date.

Core features

• Input date: enter a start date (calendar picker or typed).
• Offset: specify number of days to add (positive) or subtract (negative).
• Result date: displays the new date immediately.
• Optional include/exclude weekends: toggle to count only business days.
• Optional holiday list: exclude specified holidays when counting business days.
• Timezone handling: choose or auto-detect timezone to get accurate local results.

Common use cases

• Project deadline calculation (add N days).
• Calculate due dates for invoices or payments.
• Find a past date by subtracting days (e.g., look back N days).
• Scheduling follow-ups or reminders.
• Academic or legal timelines that require precise day counts.

How it works (brief)

1. Parse the start date into a date object.
2. If counting calendar days, add/subtract N days directly.
3. If counting business days, iterate day-by-day skipping weekends and listed holidays until N business days are reached.
4. Apply timezone rules and output in chosen format (YYYY-MM-DD, locale format).

Tips

• Use ISO format (YYYY-MM-DD) to avoid ambiguity across locales.
• When planning across timezones, set the tool to the relevant timezone to prevent off-by-one-day errors.
• For legal deadlines, confirm whether the jurisdiction counts weekends/holidays.