Select the base date to calculate from
QUICK ADD:
Ready to calculate
Select a date, choose amount & unit, then click Calculate// find the resulting date after adding or subtracting a duration
Add or subtract days, weeks, months, or years from any date. Find the resulting date instantly with weekday, week number, and full breakdown. Free, browser-based.
Ready to calculate
Select a date, choose amount & unit, then click CalculateSelect the base date you want to add or subtract from using the date picker.
Choose Add or Subtract, enter a number, then select Days, Weeks, Months, or Years.
Click Calculate to instantly see the resulting date with weekday, week number, and more.
This tool calculates the resulting date after adding or subtracting a specific duration from any starting date. Unlike simple day counters, it supports days, weeks, months, and years — correctly handling month-end edge cases and leap years.
Adding days always adds exactly that many calendar days. Adding months moves the month forward by N and keeps the same day number when possible — so adding 1 month to January 31 gives February 28 (or 29 in a leap year), not March 2nd.
Yes. The calculation uses JavaScript's native Date object which correctly accounts for leap years. Adding 1 year to February 29, 2024 will give February 28, 2025, not March 1.
ISO 8601 is the international standard for date representation: YYYY-MM-DD. For example, April 18, 2026 is written as 2026-04-18. It's unambiguous and widely used in software, APIs, and databases.
The ISO week number (ISO 8601) is used, where weeks start on Monday and the first week of the year contains the year's first Thursday. Week 1 can begin in late December of the previous year.
Absolutely. Switch the operation to "Subtract" and enter any amount in days, weeks, months, or years. The calculator works for both future and past dates with no practical limit.
This field shows how many days the resulting date is from today's date. A positive number means the result is in the future; a negative number means it's in the past.
Yes — it's commonly used for legal notice periods, contract deadlines, subscription renewal dates, and project milestones. For strict business-day counts (excluding weekends/holidays), use the Business Days Calculator instead.
The tool supports any date within JavaScript's Date object range — roughly from year 100 to year 275,760. For all practical purposes, there's no meaningful limit on how far you can add or subtract.
Whether you're planning a project deadline, calculating a legal notice period, estimating a delivery date, or figuring out when a subscription renews, the ability to add or subtract days (or weeks, months, and years) from a specific date is an essential everyday calculation. Our free Add / Subtract Days Calculator handles all of this in seconds — right in your browser, with no registration required.
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At first glance, adding 30 days to a date seems trivial. But date arithmetic is full of edge cases that trip up manual calculations: months have different lengths, leap years add an extra day in February, and the concept of "1 month from January 31" is ambiguous without a clear rule. Our calculator uses standard programming conventions — the same rules used by virtually every operating system and programming language — to produce correct, unambiguous results every time.
To add days to a date, simply: (1) select your start date using the date picker, (2) choose "Add" as the operation, (3) enter the number of days you want to add, and (4) make sure "Days" is selected as the unit. Click Calculate, and the resulting date appears instantly along with full details like the weekday name, week number, and how many days from today that date falls.
Subtracting days works identically — just switch the operation selector to "Subtract." This is useful for counting backwards: for example, "what date was 90 days ago?" is a common question in legal, medical, and financial contexts. The tool handles this just as cleanly as forward calculations.
Beyond days, the calculator supports three additional units:
The result panel provides a comprehensive breakdown of the resulting date:
YYYY-MM-DD format used in APIs, databases, and spreadsheetsProject management: Calculate a deadline 45 days from contract signing, or find when a 90-day probation period ends. Legal and compliance: Many legal deadlines are specified in calendar days — "respond within 30 days of notice." Our calculator gives you the exact date without guessing. Healthcare: Follow-up appointments, medication courses, and test result timeframes are often specified in days or weeks. Finance and subscriptions: Trial periods, billing cycles, and interest calculation periods all involve date arithmetic. Shipping and logistics: Estimate delivery windows by adding the expected transit time to a ship date.
For the most common calculations, the tool provides one-click preset buttons: +7 days, +14 days, +30 days, +90 days, and +1 year. These are the durations most frequently needed in everyday date planning. Clicking any preset automatically updates the amount and unit fields and triggers the calculation instantly.
The ISO week number shown in the results follows the ISO 8601 standard, where weeks run Monday through Sunday and the first week of the year is the one containing the year's first Thursday. This means week 1 sometimes starts in late December of the previous year. ISO week numbers are widely used in business planning, manufacturing, and logistics contexts — particularly in Europe — where "week 43" is a more natural way to refer to a span of time than giving a specific date range.
When adding months, the calculator follows the "last day of month" clamping rule used by most programming languages and spreadsheet applications. For example: adding 1 month to March 31 gives April 30 (not May 1), because April only has 30 days. Adding 1 month to January 31 gives February 28 in a common year or February 29 in a leap year. This behavior is intentional and matches the convention used by Python's dateutil, JavaScript's date-fns, PHP's DateTime, and most other date libraries.
Some of the most common date arithmetic questions people search for: "What is 30 days from today?", "What date is 90 days from now?", "What was the date 60 days ago?", "Add 6 months to a date", "What day of the week will [date] be?" — all of these are trivially answered by this tool. Bookmark it for quick access whenever you need a reliable date calculation.