Date Calculator

A date calculator finds the date a set number of days away, or counts the days between two dates. To find 90 days after January 1, 2026, count through the calendar: 30 days are left in January, February adds 28, March adds 31, and 1 more day reaches Wednesday, April 1, 2026. The tool below does the same count from your own today.

How to use the date calculator

1. Pick a calculation: days from today, days between two dates, add or subtract time, or the day of the week.
2. For “days from today,” tap 30, 60, 90 or 180 days, or type any number. Choose Before to count back in time.
3. Pick dates with the date boxes. The Today link fills in today’s date from your device.
4. Read the answer at the top of the green box, then open Show steps to see the count month by month. Copy result puts the answer on your clipboard.

Results also show business days, weeks and days, and the ISO date. If an answer lands on a weekend or holiday, the next business day appears under it. Add / subtract lists up to 6 repeats, such as every two weeks.

How to count the days between two dates

Break the span into three pieces: the days left in the first month, the whole months in between, and the days into the last month. From March 14 to July 4, 2026:

• Days left in March after the 14th: 31 − 14 = 17.
• Whole months: April 30 + May 31 + June 30 = 91.
• Days into July: 4.

The total is 17 + 91 + 4 = 112 days, which is exactly 16 weeks.

Should you include the end date?

By default the count gives the number of days that pass: from Monday to Tuesday is 1 day. That is the usual meaning for ages and deadlines. If you are counting days on a schedule, such as a hotel booking or an event that runs from the 1st to the 4th, you want both dates counted, so tick Include the end date. It adds exactly 1 day: the 1st to the 4th is 3 days elapsed, or 4 days counted.

Adding days, weeks, months and years to a date

Days and weeks are simple, because every day has the same length: add the days and roll into the next month when you pass its last day. Months and years are trickier, because months are 28 to 31 days long.

The calculator adds months by changing the month and keeping the day number. When that day does not exist in the new month, it uses the month’s last day. This is the month-end rule:

• January 31, 2026 + 1 month = February 28, 2026, because February 2026 has only 28 days.
• January 31, 2024 + 1 month = February 29, 2024, because 2024 is a leap year.
• February 29, 2024 + 1 year = February 28, 2025.

Order matters near the end of a month. The calculator adds years and months first, then weeks and days. January 30, 2026 plus 1 month is February 28, and 1 more day gives March 1. If you added the day first, you would get January 31, and 1 month later is February 28. The steps always say which order was used.

Business days and federal holidays

Business days are Monday to Friday. Tick Also skip US federal holidays to also remove the 11 federal holidays. A holiday that falls on a Saturday is observed on the Friday before, and one on a Sunday on the Monday after. State, school and company holidays are never removed.

Counting starts the day after the start date. From Friday, October 30, 2026 to Monday, November 2, 2026 is 3 calendar days but only 1 business day, the Monday. 90 business days after Thursday, January 1, 2026 is Thursday, May 7, 2026, or Monday, May 11, 2026 once Martin Luther King Jr. Day and Washington’s Birthday are skipped.

New Year’s Day 2028 falls on a Saturday, so it is observed on Friday, December 31, 2027.

Worked date examples

Example 1: 90 days from October 31, 2026

October 31 is the last day of the month, so no days are left in October. November adds 30 and December adds 31, which makes 61. You need 90 − 61 = 29 more days, so the answer is January 29, 2027. Since 90 = 12 × 7 + 6, the weekday moves 6 days forward, from Saturday to Friday.

Example 2: Days until Christmas

From October 31, 2026 to December 25, 2026: no days are left in October, November has 30, and December adds 25. That is 55 days, or 7 weeks 6 days.

Example 3: The day of the week for July 4, 1776

Zeller’s congruence gives the weekday for any Gregorian date: h = (q + ⌊13(m + 1)/5⌋ + K + ⌊K/4⌋ + ⌊J/4⌋ + 5J) mod 7, where q is the day, m the month, K the last two digits of the year and J the century part. For July 4, 1776: q = 4, m = 7, K = 76, J = 17. The pieces are 4 + 20 + 76 + 19 + 4 + 85 = 208, and 208 mod 7 = 5, which stands for Thursday (0 = Saturday, 1 = Sunday, and so on). January and February count as months 13 and 14 of the previous year.

Days from a date: quick reference table

This table uses January 1, 2026 as a fixed start date. The calculator above builds the same table from your own today.

Leap years and month lengths

April, June, September and November have 30 days. February has 28 days, or 29 in a leap year. The rest have 31. Under the Gregorian calendar, a year is a leap year if it divides evenly by 4, except century years, which must also divide evenly by 400. So 2024 and 2000 were leap years, while 1900 was not and 2100 will not be. A common year has 365 days and a leap year has 366.

Common date counting mistakes

• Counting the start day. If today is the 1st, then 10 days from today is the 11th, not the 10th.
• Treating a month as 30 days. “Three months” from January 31 is April 30, but 90 days from January 31 is May 1 in 2026.
• Forgetting February 29 when a range crosses the end of February in a leap year.
• Assuming business days skip holidays. Most date tools skip only weekends unless they say otherwise. Here, tick the federal holiday box.
• Using the wrong “today.” Near midnight, today may already be tomorrow in another time zone. The calculator uses your device’s date.

Sources

• U.S. Naval Observatory: Leap years
• U.S. Office of Personnel Management: What are federal holidays?
• U.S. Office of Personnel Management: Federal holidays (observed dates by year)
• U.S. Office of Personnel Management: Federal holidays that fall on a Saturday or Sunday

Date counting practice quiz: 10 questions

Test yourself with 10 multiple-choice questions. Choose an answer and press Submit to see if you are right and why. Your score appears at the end.

Frequently asked questions

What date is 90 days from today?

It depends on today's date, so use the 90 days button above; it reads the date from your device. As an example, 90 days from Saturday, October 31, 2026 is Friday, January 29, 2027. Ninety days is 12 weeks and 6 days, so the weekday moves 6 days forward.

Do you count the first day when counting days?

Usually not. "Days between" and "days from" count the days that pass, so the start date is day 0 and the next day is day 1. If you need both the first and last day counted, add 1 or tick Include the end date.

How many weeks is 90 days?

Divide by 7: 90 ÷ 7 = 12 remainder 6, so 90 days is 12 weeks and 6 days.

How many business days are in a year?

A year has 260 to 262 weekdays, depending on which day it starts on and whether it is a leap year. 2026 has 261 weekdays, or 250 after the 11 federal holidays. Subtract any other holidays your workplace observes.

What is January 31 plus one month?

There is no February 31, so the date moves to the last day of February: February 28, or February 29 in a leap year. Spreadsheet month functions such as EDATE in Excel follow the same rule.

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