Add or Subtract Days Calculator — Warranty Expirations & Net 30/60 Invoices

Add or subtract days, weeks, months, or years from any starting date. Calculate invoice payment due dates (Net 30/60), warranty expiration dates, and court deadlines.

Subtract Mode vs Difference Mode

Subtract Mode counts backwards from a single Start Date (e.g. "What date was 90 days ago?"). Difference Mode compares two specific dates to measure the exact calendar and business days between them.

Start Date

Time Units to Add / Subtract

Years

Months

Weeks

Days

Subtract Mode (Count Backwards)

Business Days Only (Mon-Fri)

Resulting Target Date

Including all calendar days

Quick Presets

Major Countdowns

Standard Calendar Offsets

Offset	Resulting Date

Business Day Offsets

Work Days	Resulting Date

Overview & Capabilities

The Add or Subtract Days Calculator helps corporate accountants, legal clerks, supply chain logisticians, and healthcare professionals project future deadlines or historical dates from a fixed reference point. When establishing a commercial Net 30 or Net 60 invoice payment due date, calculating a statutory 90-day court filing deadline, or finding the exact expiration date of a 2-year warranty, this tool instantly computes the target calendar date.

Tutorial

How to Use

Select your starting reference Date.

Choose whether to Add (+) or Subtract (-) time.

Enter the quantity of days, weeks, months, or years to adjust.

Optionally toggle business working days to skip weekends and holidays.

View the calculated target calendar date along with the day of the week and ISO week number.

Capabilities

Key Features

Bidirectional date projection (add future days or subtract past intervals)

Flexible multi-unit adjustment (add combinations of days, weeks, months, and years)

Day of the week and ISO week number resolution for target dates

Instant calendar calculation with leap-year and month-end boundary handling

Applications

Common Use Cases

Commercial Invoice Due Dates: Add 30 or 60 days to an invoice issue date to calculate exact Net 30/Net 60 payment deadlines.

Product Warranty Expiration: Add 365 or 730 days to a purchase receipt date to determine when customer warranty coverage lapses.

Prescription Refill Scheduling: Add 90 days to a pharmacy prescription issue date for automated refill reminders.

Guidance

Tips & Best Practices

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When adding months to the 31st of a month, the calculator automatically snaps to the last valid day of shorter months (e.g. Jan 31 + 1 month = Feb 28/29).

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Combine weeks and days for complex scheduling (e.g. 6 weeks and 3 days).

Answers

Frequently Asked Questions

Q What date is 30 days from today?

The calculator automatically loads today's date, allowing you to view the exact date 30 days ahead with one click.

Q How does adding a month to January 31st work?

The calculator resolves to the last valid day of February (February 28th, or February 29th in a leap year).

Q Can I subtract days to find a past date?

Yes, select the "Subtract" option to calculate what date occurred a specific number of days, weeks, or months ago.

Q Does the calculator show what day of the week the target date falls on?

Yes, the target date displays the full day of the week (e.g. "Tuesday, October 14, 2026") to avoid weekend deadline conflicts.