Add Days to Date Calculator
Find the exact future date by adding a number of days to any starting point. Perfect for shipping estimates, contract expirations, project deadlines, and personal planning. Includes a business days mode that skips weekends and holidays — and handles leap years automatically. Free, private, and runs entirely in your browser.
What does this add days calculator do?
This tool finds the exact date that lies a specified number of days in the future from any starting date. Enter a start date, type how many days you want to move forward, and the calculator rolls the calendar ahead instantly. It's the natural counterpart to subtracting days from a date, and it's useful for a surprising number of everyday tasks.
Common uses include: working out when a payment is due under Net 30 or Net 60 terms, calculating a shipping arrival date from a carrier's "3–5 business days" estimate, finding the expiration date of a warranty or subscription, or simply figuring out what day it will be 90 days from today. The calculator handles all the messy parts — month boundaries, leap years, different month lengths — so you don't have to count forward on a calendar.
For situations where only working days count (like contract deadlines or shipping estimates), switch to Business Days mode. That mode skips weekends and any custom holidays you specify, so the result always lands on a working day.
How to add days to a date
- Choose your mode: Calendar Days adds every day in the calendar. Business Days skips weekends and holidays, counting only working days.
- Enter the start date: Pick the date you want to count forward from. This is the "anchor" date.
- Enter the number of days: Type how many days you want to add. For example, 30 for a month, 90 for a quarter, or 365 for a year.
- Add holidays (Business Days mode only): Paste any dates you want to skip, one per line. Public holidays, company closures, personal days — anything that shouldn't count as a working day.
- Click Add Days: The result date appears immediately, with a full breakdown showing the start date, days added, and (in business days mode) how many weekends and holidays were skipped.
Why use this calculator?
Two modes in one
Add plain calendar days or switch to business days mode to skip weekends and holidays. Both modes handle any date range you throw at them.
Leap year handling
Correctly handles leap years, month lengths, and the century rule (years divisible by 100 are not leap years unless also divisible by 400).
Custom weekend support
Not everyone works Monday to Friday. Click the day chips to define your own weekend — Friday–Saturday, Sunday only, or any combination.
Holiday exclusion
Paste your holiday list, one date per line, and the business days mode will skip them automatically so your count is accurate.
100% private
Everything runs in your browser. No dates are sent to a server. Close the tab and the data is gone.
Works offline
Once the page loads, the calculator keeps working without an internet connection. Perfect for flights or remote areas.
Common use cases for adding days
Invoices and payments
- Net 30 / Net 60 terms: If an invoice is issued today, add the payment term to find the due date.
- Late fee start dates: Determine when a late fee kicks in by adding the grace period to the invoice date.
- Interest accrual: Find the date from which interest begins to accrue on an overdue balance.
Shipping and logistics
- Delivery estimates: Convert a "3–5 business days" shipping estimate to an actual expected arrival date.
- Dispatch planning: Find the last date to ship an order so it arrives before a customer deadline.
- Return windows: Determine the final date a customer can return an item by adding the return period to the delivery date.
Legal and contracts
- Notice periods: If a lease requires 60 days' notice, add 60 days to the notice date to find the effective termination date.
- Contract expirations: Calculate when a fixed-term agreement ends by adding the term length to the start date.
- Warranty periods: Find the exact expiration date of a warranty by adding the warranty term to the purchase date.
Project management
- Deadline forecasting: Set realistic deadlines by adding estimated durations to a project kickoff date.
- Sprint planning: Calculate sprint end dates by adding working days to the sprint start.
- Milestone tracking: Map out milestone dates by chaining day additions across a project timeline.
Personal planning
- Subscription renewals: Find the next renewal date by adding the billing cycle to the last payment date.
- Event countdowns: See what day it will be 100 days from now for a milestone or habit tracker.
- Vacation planning: Work out when your leave days end by adding the number of leave days to the start date.
Calendar days vs business days: which should you use?
The choice between calendar days and business days matters more than most people realize. Getting it wrong can mean missing a deadline by several days.
| Scenario | Use Calendar Days | Use Business Days |
|---|---|---|
| Shipping estimate ("3–5 days") | Yes — most carriers count working days | |
| Legal notice period | Yes — courts typically count business days | |
| Invoice due date (Net 30) | Sometimes | Sometimes — depends on the contract |
| Warranty period | Yes — usually calendar-based | |
| Return window | Yes — usually calendar-based | |
| Project sprint duration | Yes — teams usually work business days | |
| Personal countdown ("100 days from now") | Yes |
When in doubt, check the contract or policy language. If it says "days," it usually means calendar days. If it says "business days" or "working days," switch the calculator to business days mode and adjust the weekend settings to match the relevant jurisdiction.
How leap years affect your calculation
Leap years add an extra day (February 29) to the calendar. When you add days across a leap year boundary, the result can differ by one day compared to a non-leap year. This calculator handles that automatically, but it's worth understanding the rule:
- A year is a leap year if it is divisible by 4.
- But years divisible by 100 are not leap years — unless they are also divisible by 400.
- So 2000 was a leap year (divisible by 400), but 1900 was not.
For example, if you add 365 days to March 1, 2023, you get February 29, 2024 (because 2024 is a leap year). Add 365 days to March 1, 2024, and you get March 1, 2025 — because 2024 already included the extra day. The calculator gets this right every time.