Date Calculator (Days Between Dates)

What does this date calculator count?

A date calculator answers two everyday questions. How many days lie between two dates, and which date do you reach after a given period? This one handles both in a single panel. In the first mode you pick two dates. You then see the day count, a weeks and days split, working days, weekend days and the gap in years, months and days. In the second mode you add or subtract days, workdays, weeks, months or years. The resulting date then arrives with its weekday.

• Between two dates: days left until an exam, a delivery or New Year.
• Add or subtract: the date 90 days from now, 10 workdays from now or six months ago.

I use it most in two places. First, I plan the length and budget of ad campaigns with it. Second, I agree web project deadlines in working days. Counting by hand goes wrong fast, because months run from 28 to 31 days. On top of that, 29 February turns up every four years. The tool counts on the real calendar instead. It also runs entirely in your browser, so the dates you pick never reach a server.

For an exact age from a birth date, the age calculator shows the same years, months and days logic in more detail.

Exclusive or inclusive counting: which one fits your case?

By default the tool leaves out the start day and counts the end day. So Monday to Tuesday gives 1 day. That choice mirrors how legal deadlines work. For example, Rule 6(a) of the US Federal Rules of Civil Procedure excludes the day of the triggering event. It then counts every day and includes the last day of the period. The EU Regulation 1182/71 on time limits follows the same idea. The day on which the event occurs does not fall within the period.

Other questions need both ends. In those cases tick 'Count the start day too':

• Inclusive: days of leave, campaign or event runs, the total days in a quarter.
• Exclusive: hotel nights, how many days until a subscription or lease runs out, periods that start after a delivery.

Ticking the box adds 1 calendar day, and it adds 1 working day when the start date is a weekday. If you compare with Excel, keep in mind that NETWORKDAYS counts both the start and the end date. So tick the box whenever you want this tool to match that spreadsheet figure.

Why doesn't the tool subtract public holidays?

The tool counts Monday to Friday as working days and leaves public holidays in. The reason is practical: holiday calendars change by country, by year and even by region. In the UK, for instance, the official bank holiday list differs between England and Wales, Scotland and Northern Ireland. In the US, federal holidays, state holidays and company closures rarely match one another.

So the safest routine has three steps:

1. Take the working-day count from the tool.
2. Look up the holidays that fall on weekdays inside your range.
3. Subtract them yourself and note which calendar you used.

Deadlines add one more rule. Under Rule 6(a), a period that ends on a Saturday, Sunday or legal holiday runs on. It continues to the next day that is none of those. Regulation 1182/71 does the same for EU acts and moves the end to the following working day. In other words, the calendar date the tool shows is the starting point, not always the final legal deadline. For anything with legal weight, check the current rules or ask a professional.

Why does the end date shift when you add months or years?

Adding a month is not the same as adding 30 days. When you add months or years, the tool keeps the day number: 15 March plus one month gives 15 April. If the target month has no such day, the result drops to the last day of that month. So 31 January 2027 plus one month returns 28 February 2027, because 2027 is not a leap year.

The EU rules on time limits work the same way. Take a period in months or years whose last day does not exist in the final month. Regulation 1182/71 then ends it on the last day of that month. Leap days follow the same logic, so 29 February 2028 plus one year returns 28 February 2029.

• If the terms say '30 days', choose days as the unit.
• When the contract speaks of 'one month', pick months instead.
• For wording like 'within 10 working days', select workdays; the tool then skips weekends.

The difference looks small, yet it moves payment dates, trial periods and subscription renewals by a day or two. That is why I suggest you read the exact wording first and choose the unit to match it.

Using a date calculator for ad campaign schedules

In Google Ads management, the calendar sets the budget. According to Google Ads Help, the monthly spending limit for most campaigns is 30.4 times the average daily budget. On a single day, spend can reach twice that average. As an example calculation, a campaign with a £50 daily budget spends at most £1,520 in a month.

When I plan a campaign, I use the tool in this order:

• Enter the start and end dates with the start day counted to get the total days live.
• Divide the total budget by that number to find the daily budget.
• Pick report periods of equal length with the same weekday mix; 28 days is exactly 4 weeks, which makes comparisons fair.

I explain budget setting in my guide to Google Ads budgets and period comparisons in how to read a digital marketing report. To check the return of a campaign, try the ROAS calculator. If you want help planning campaigns, see our Google Ads management page.

How do you plan project deadlines in working days?

When I agree timelines for web design projects, I talk in working days, because calendar days include weekends and inflate expectations. For example, take a job that starts on Thursday 1 October 2026 and needs 10 working days. It finishes on Thursday 15 October 2026, 14 calendar days later.

Here is the order I recommend:

1. Split the work into phases and give each phase a length in working days.
2. Find each phase end in 'Add or subtract' mode with workdays as the unit.
3. Take out public holidays in between and move the date to the next working day.
4. Add waiting time for approvals and feedback as separate phases.

I list the phases of a business website in the corporate website design process. SEO expectations are a timeline question too, and I discuss realistic ranges in how long SEO takes. If you are planning a new project, take a look at our web design service.

What is an ISO week number, and why do some years have 53 weeks?

In the add or subtract mode, the last row shows the ISO 8601 week number of the resulting date. Under this standard a week starts on Monday, and week 1 is the week that contains the year's first Thursday. Weekly reports, production plans and a lot of European business mail rely on this number.

The rule brings a surprise now and then. Because 1 January 2026 fell on a Thursday, 2026 has 53 ISO weeks. For example, add 90 days to 5 October 2026 and the tool returns Sunday 3 January 2027 with 'Week 53 (2026)'. The year in brackets tells you the week belongs to a week year that differs from the calendar year.

• January's first days can fall into the last week of the previous year.
• Likewise, the last days of December can move into week 1 of the next year.
• In weekly comparisons, it is safer to note the date range next to the week number.

If you build weekly ad reports, tag your campaign links with the UTM builder. That way you can tell which source worked in which week.