Time and Date Calculators

Choosing the right time or date calculator

Counting between two dates. Use the days between dates calculator when you know both dates and want the gap: days until a deadline, the length of a trip, or how many weekdays a project spans. It can count the end date or leave it out, which is the most common source of off-by-one disagreements.

Finding a date. Use the date calculator when you know a start date and a length of time and want the date it lands on, such as 90 days from today or 6 months after a contract starts.

Ages. The age calculator is a special case of counting between dates. It gives an age in completed years, months and days, as people normally state it, along with the total in weeks and days and the date of the next birthday.

Hours in a day. The hours calculator works with clock times rather than dates. It finds the time between a start and an end time, handles shifts that run past midnight, subtracts an unpaid break and converts the result to decimal hours for timesheets.

The calculators at a glance

• Days between dates calculator: the number of days between two dates, with or without the end date, plus the gap in years, months and days, in weeks, and as weekdays and weekend days.
• Date calculator: add or subtract days, weeks, months or years from any date and see the day of the week it falls on.
• Age calculator: an exact age on today’s date or any other date, with totals in months, weeks and days and the countdown to the next birthday.
• Hours calculator: time worked between a start and an end time, minus an unpaid break, in hours and minutes and in decimal hours.

How these calculators handle dates

All of the date calculators follow the same rules, so their answers agree with each other.

• Calendar dates only. Dates are treated as whole days with no time of day and no time zone, so results don’t shift with daylight saving time or where you are.
• The start date is day 0. Adding 1 day gives the next day, and the count between two dates leaves out the end date unless you ask for it to be included.
• Real month lengths. Months are counted on the calendar rather than as 30 days. When a date doesn’t exist in the target month, such as the 31st in April, the result moves to the last day of that month.
• Leap years. February 29 is included in leap years under the Gregorian rule, and a February 29 birthday is counted on February 28 in common years.
• No holidays. Weekends are identified, but public holidays differ by place and are left for you to subtract.

Glossary

• Inclusive count. A day count that includes both the start and end dates. It is always one more than the exclusive count.
• Exclusive count. A day count from the start date up to, but not including, the end date. Used for gaps and countdowns.
• Business day. A working day, usually Monday to Friday excluding public holidays.
• Leap year. A year with 366 days. Years divisible by 4 are leap years, except century years not divisible by 400.
• Completed age. The number of full years since birth, which is how age is normally stated.
• Decimal hours. Hours written as a decimal number for payroll, such as 7.5 for 7 hours 30 minutes.

Guides

• How leap years work explains the Gregorian leap year rule, why 2100 won’t be a leap year, and how February 29 affects day counts, date arithmetic and birthdays.
• How to calculate hours worked walks through a timesheet from clock times to a weekly total, covering overnight shifts, unpaid breaks, decimal hours and rounding.

For working with the numbers these calculators produce, the math calculators include percentages, fractions and averages, and the finance calculators cover interest and loans, where the length of a period in days or months often matters.