By the Age-Finder team · Last updated 7 November 2026
Quick answer
Work out the date 90 days from today, Saturday 7 November 2026: it is Friday, 5 February 2027. Enter a start date, choose Add or Subtract, and type the years, months, weeks and days; months move first, then the days.
The Date Calculator adds or subtracts any mix of years, months, weeks and days from a start date and shows the exact calendar date you land on, with its weekday. Leave the start date empty to count from today.
How to Use the Date Calculator
Choose a start date, or leave it blank to start from today. Pick Add or Subtract. Type the years, months, weeks and days you need. Any of them can be left empty.
Select Calculate. The card turns over to show the new date, how far it is from today and which day of the year it is.
If you only need to know how many days separate two dates you already have, use the Days Between Dates calculator instead. To count down to a date from today, the Countdown Calculator shows the days until it.
Common Dates From Today
Counted from today, Saturday, 7 November 2026:
| Add | Result date | Weekday | What it is used for |
|---|---|---|---|
| 30 days | 7 December 2026 | Monday | Notice periods and return windows |
| 60 days | 6 January 2027 | Wednesday | Two-month deadlines |
| 90 days | 5 February 2027 | Friday | Quarterly reviews and the 90-day rule |
| 180 days | 6 May 2027 | Thursday | Six-month trials and probation |
| 365 days | 7 November 2027 | Sunday | One year from today |
| 6 months | 7 May 2027 | Friday | Half-year reviews and renewals |
How the Calculator Adds Months and Years
Days and weeks are simple: a week is always seven days, so adding 90 days moves the date forward exactly 90 calendar days. Months and years are different, because months have 28, 29, 30 or 31 days.
The calculator follows the same rule as every page on Age-Finder: it moves the month (and year) first, keeping the same day of the month. When that day does not exist in the new month, it uses the last day of that month instead. Weeks and days are added after that.
| Start date | Change | Result | Why |
|---|---|---|---|
| 31 January 2026 | + 1 month | 28 February 2026 | February 2026 has no 31st, so the date moves to the 28th. |
| 31 January 2028 | + 1 month | 29 February 2028 | 2028 is a leap year, so February has 29 days. |
| 29 February 2024 | + 1 year | 28 February 2025 | 2025 has no 29 February. |
| 31 August 2026 | + 6 months | 28 February 2027 | February 2027 has 28 days. |
| 31 January 2026 | + 30 days | 2 March 2026 | Days are counted one by one, so the month length matters. |
The last two rows show why “1 month” and “30 days” are not the same thing. Adding a month keeps you on the same day number whenever possible. Adding 30 days counts calendar days and can land on a different day number.
Worked Examples
Adding a mix of units
Start: 1 January 2026. Add 1 year, 2 months, 3 weeks and 4 days. Move the year and months first: 1 January 2026 plus 1 year and 2 months is 1 March 2027. Add 3 weeks (21 days): 22 March 2027. Add 4 days: 26 March 2027. The result is Friday, 26 March 2027.
Counting a deadline in days
A 90-day period starting on 1 January 2026 ends on Wednesday, 1 April 2026. January has 31 days, February 28 and March 31, so 90 days after 1 January is 1 April.
Counting backwards
Subtract 6 weeks from Sunday, 15 March 2026 and you reach Sunday, 1 February 2026. Subtracting whole weeks always lands on the same weekday you started from.
Leap Years When Adding Days
Leap years change the result whenever a period crosses the end of February. Thirty days after 1 February 2026 is 3 March 2026, because February 2026 has 28 days.
Thirty days after 1 February 2028 is 2 March 2028, because 2028 is a leap year and February has 29 days. The calculator includes every leap day automatically, so you never need to check the calendar yourself.
The U.S. Naval Observatory leap years page sets out the Gregorian leap-year rule: the rule is that a year is a leap year when 4 divides it, unless it is a century year, in which case 400 must divide it.
Over a long period, such as 10 years, two or three leap days fall inside the span, which is why “10 years” and “3,650 days” lead to different dates:
1 January 2026 plus 10 years is 1 January 2036, which is 3,652 days later because 2028 and 2032 are leap years, while 1 January 2026 plus 3,650 days is 30 December 2035, two days earlier.
Business Days, Worked by Hand
The calculator counts every calendar day, weekends included. It has no business-day mode. When a deadline is written in working days, count them by hand or use the Business Days Calculator. Counting 10 business days forward from Saturday, 7 November 2026 lands on Friday, 20 November 2026.
Counting 30 business days forward lands on Friday, 18 December 2026. The 90-calendar-day span from 7 November 2026 to 5 February 2027 holds 65 business days, and the 90-calendar-day span from 1 January to 1 April 2026 holds 64 business days.
In Excel and Google Sheets
Dates are stored as numbers in a spreadsheet, so the same arithmetic works there. With the start date in A1 and the end date in B1:
| What you want | Formula | Notes |
|---|---|---|
| Add 90 days | =A1+90 |
Format the result cell as a date. |
| Subtract 90 days | =A1-90 |
Format the result cell as a date. |
| Add 6 months | =EDATE(A1,6) |
Moves to the last day of the month when needed, like this calculator. |
| Add 1 year | =EDATE(A1,12) |
Twelve months, with the same month-end rule. |
| Days between two dates | =B1-A1 |
Format the cell as a number. |
| Working days between two dates | =NETWORKDAYS(A1,B1) |
Counts both ends, Monday to Friday only. |
| A date 30 working days later | =WORKDAY(A1,30) |
Skips Saturdays and Sundays. |
Finding a Date in the Past
Choosing Subtract answers “what was the date X years ago?” questions. Subtracting 18 years from 6 November 2026 gives Thursday, 6 November 2008: anyone born on or before that date has turned 18 by 6 November 2026.
For an exact age on a particular day rather than a date, use the Age on a Specific Date calculator.
Adding Days or Adding Months: Which to Use
Use the unit that your rule is written in: If a contract, notice period or policy says “30 days”, add 30 days. If it says “one month”, add one month.
If it says “business days” or “working days”, weekends and public holidays are excluded, which this calculator does not do. Count those separately. If it says “within one year”, add one year, and remember that 29 February start dates move to 28 February in common years.
When a rule is ambiguous, check how the organisation that wrote it counts. Some legal and financial systems have their own conventions for month ends and for whether the start day is included.
Everyday Uses
Working out the date a notice period, trial period or return window ends. Finding the date 6 months or 1 year after a start date, such as a review, renewal or anniversary.
Planning events a set number of weeks ahead. Checking the date a set number of years ago for an age cut-off. Counting forward from a purchase date to find when a warranty or subscription runs out.
What other date calculators offer
Most date calculators on the first page add and subtract days, weeks, months and years the same way this one does. What sets them apart is the business-day counting and the extras they show. The comparison below is against the three date calculators that rank highest.
| Feature | Age-Finder | EverydayTools | NeftCal | Calculations.tools |
|---|---|---|---|---|
| Add or subtract years, months, weeks and days | Yes | Yes | Yes | Yes |
| Result date with its weekday | Yes | Yes | Yes | Yes |
| Day of the year of the result | Yes | Not shown | Not shown | Not shown |
| ISO week number of the result | No | Not shown | Yes | Yes |
| Days between two dates in the same tool | No | Yes | Not shown | Yes |
| Business-day mode | No, in the guide | Yes, US weekday calendar | Not shown | Yes, workdays Mon-Fri |
| Preset chips for common counts | No | Not shown | Yes, +7, +30, +90, +1 year | Not shown |
| Free, no download or account | Yes | Yes | Yes | Yes |
The shortfalls, in plain words: the tool has no business-day mode and no between-dates mode, it shows no ISO week number for the result, and it offers no preset chips for common counts.
What it adds is the day of the year of the result and the month-end clamp note, with business days and spreadsheet formulas covered in the guide instead.
Frequently Asked Questions
What is 31 January plus one month?
28 February, or 29 February in a leap year. February never has 31 days, so the calculator uses the last day of February, the same rule used across Age-Finder.
Is adding one month the same as adding 30 days?
No. One month keeps the same day number where possible (15 March plus one month is 15 April), while 30 days counts calendar days one by one and can land on a different day number.
Can I subtract dates as well as add them?
Yes. Choose Subtract, and the calculator counts backwards by the years, months, weeks and days you enter.
What is the date 100 days from today?
Leave the start date empty, choose Add and type 100 in Days. For example, 100 days after Friday, 6 November 2026 is Sunday, 14 February 2027.
Does the calculator include the start date?
The result is the date you reach after moving forward or backward by the amount you enter, so the start date itself is day zero. Adding 1 day to 6 November gives 7 November.
Does it skip weekends or holidays?
No. It counts every calendar day. Business-day counts exclude weekends and public holidays, which vary by country.
Sources
- The U.S. Naval Observatory leap years page sets out the Gregorian leap-year rule used on this page.
- Age-Finder methodology (the month-end rule used on every calculator).