Days in Each Month
A quick reference for how many days are in each month of the year. Whether you are doing date calculations, planning schedules, or counting days for a project deadline, knowing exact month lengths is essential. This guide includes cumulative day-of-year values, business day counts for 2026, and the history behind why months have different lengths.
- 31 days: January, March, May, July, August, October, December (7 months)
- 30 days: April, June, September, November (4 months)
- 28/29 days: February (29 in leap years)
- Total: 365 days per year (366 in leap years)
Complete Month Reference
The following table shows the number of days in each month along with its quarter and the day-of-year range starting from January 1:
| Month | Days | Quarter | Days from Jan 1 |
|---|---|---|---|
| January | 31 | Q1 | 0-31 |
| February | 28/29 | Q1 | 31-59 |
| March | 31 | Q1 | 59-90 |
| April | 30 | Q2 | 90-120 |
| May | 31 | Q2 | 120-151 |
| June | 30 | Q2 | 151-181 |
| July | 31 | Q3 | 181-212 |
| August | 31 | Q3 | 212-243 |
| September | 30 | Q3 | 243-273 |
| October | 31 | Q4 | 273-304 |
| November | 30 | Q4 | 304-334 |
| December | 31 | Q4 | 334-365 |
| Total | 365/366 |
Cumulative Day-of-Year Table
This table is useful for converting any date to its day-of-year number, which simplifies calculating days between dates. To find the day-of-year for a specific date, add the day of the month to the cumulative total for that month's start.
| Month | Start Day (Non-Leap) | End Day (Non-Leap) | Start Day (Leap) | End Day (Leap) |
|---|---|---|---|---|
| January | 1 | 31 | 1 | 31 |
| February | 32 | 59 | 32 | 60 |
| March | 60 | 90 | 61 | 91 |
| April | 91 | 120 | 92 | 121 |
| May | 121 | 151 | 122 | 152 |
| June | 152 | 181 | 153 | 182 |
| July | 182 | 212 | 183 | 213 |
| August | 213 | 243 | 214 | 244 |
| September | 244 | 273 | 245 | 274 |
| October | 274 | 304 | 275 | 305 |
| November | 305 | 334 | 306 | 335 |
| December | 335 | 365 | 336 | 366 |
For example, March 15 in a non-leap year is day 60 + 14 = day 74. In a leap year, it would be day 61 + 14 = day 75.
Business Days per Month in 2026
When planning work schedules, payroll, or project timelines, you need to know how many business days (weekdays minus federal holidays) each month contains. Here is the breakdown for 2026:
| Month | Calendar Days | Weekdays | Holidays | Business Days |
|---|---|---|---|---|
| January | 31 | 22 | 2 | 20 |
| February | 28 | 20 | 1 | 19 |
| March | 31 | 22 | 0 | 22 |
| April | 30 | 22 | 0 | 22 |
| May | 31 | 21 | 1 | 20 |
| June | 30 | 22 | 1 | 21 |
| July | 31 | 23 | 1 | 22 |
| August | 31 | 21 | 0 | 21 |
| September | 30 | 22 | 1 | 21 |
| October | 31 | 22 | 1 | 21 |
| November | 30 | 21 | 2 | 19 |
| December | 31 | 23 | 1 | 22 |
| Total | 365 | 261 | 10 | 251 |
Use our business days calculator to count working days between any two dates.
Memory Trick
There are two well-known methods for remembering how many days each month has without looking at a reference table.
The Classic Rhyme
"Thirty days has September,
April, June, and November.
All the rest have thirty-one,
Except February alone,
Which has twenty-eight days clear,
And twenty-nine in each leap year."
This rhyme has been used since at least the 16th century and remains one of the most reliable memory aids for month lengths.
Knuckle Method
Make a fist with your left hand and count across the knuckles and valleys, starting from the left:
- First knuckle: January (31)
- First valley: February (28/29)
- Second knuckle: March (31)
- Second valley: April (30)
- Third knuckle: May (31)
- Third valley: June (30)
- Fourth knuckle: July (31)
After July, start back at the first knuckle for August (31), and continue the pattern through December. Every knuckle (high point) is a 31-day month, and every valley (low point) is a 30-day month — except February.
Why Do Months Have Different Lengths?
The irregular arrangement of month lengths dates back to ancient Rome. The original Roman calendar, attributed to Romulus around 753 BC, had only 10 months totaling 304 days. The months of January and February were added later by King Numa Pompilius to bring the calendar closer to the solar year.
When Julius Caesar reformed the calendar in 45 BC to create the Julian calendar, months were given alternating lengths of 31 and 30 days, with February receiving 29 days (30 in leap years). However, when the month of Sextilis was renamed to August in honor of Emperor Augustus, it was given 31 days to match July (named after Julius Caesar). This required taking a day from February, giving it 28 days in regular years.
The result is the somewhat irregular pattern we still use today: seven months with 31 days, four with 30, and February with 28 or 29.
The Gregorian Calendar
The calendar system used by most of the world today is the Gregorian calendar, introduced by Pope Gregory XIII in 1582. It refined the Julian calendar by adjusting the leap year rules to better match the solar year of approximately 365.2422 days.
The Gregorian reform did not change the number of days in each month. Instead, it corrected the cumulative drift caused by the Julian calendar's slightly inaccurate leap year rule. Under the Gregorian system:
- Years divisible by 4 are leap years
- Century years (1700, 1800, 1900) are not leap years unless also divisible by 400
- This means 2000 was a leap year, but 1900 was not
For more details on leap years, see our complete leap year guide.
How Month Lengths Affect Date Calculations
Varying month lengths are the main reason date arithmetic is not straightforward. When you need to add days to a date or subtract days from a date, you must account for the specific number of days in each month the calculation crosses.
For example, adding 30 days to January 15 gives you February 14 — but adding 30 days to January 31 gives you March 2 (or March 1 in a leap year), because February has only 28 or 29 days. This is why using a date calculator is more reliable than mental math for date calculations.
Key considerations:
- Adding months vs. adding days: "One month from January 31" could be February 28 or March 3 depending on interpretation
- Billing cycles: Monthly billing on the 31st skips February and short months
- Deadlines: "90 calendar days" is not the same as "3 months" in most cases
- Leap year crossings: Any calculation crossing February must check for leap years
Frequently Asked Questions
February has 28 days in a regular year and 29 days in a leap year. Leap years occur every 4 years (with exceptions for century years not divisible by 400). The next leap year is 2028, when February will have 29 days.
The varying month lengths are a legacy of the Roman calendar. The original 10-month calendar was expanded to 12 months, and subsequent rulers like Julius Caesar and Augustus adjusted individual months for political and practical reasons. The result is 7 months with 31 days, 4 with 30, and February with 28 or 29.
Make a fist and count across your knuckles. Starting from the index finger knuckle: each knuckle represents a 31-day month, each valley between knuckles a shorter month. Start with January on the first knuckle, February in the valley, and continue through July on the last knuckle. Then restart at the first knuckle for August.
A regular year has 365 days. A leap year has 366 days. The total comes from adding all month lengths: (7 x 31) + (4 x 30) + 28 = 365. For a detailed breakdown, see our days in a year guide.
Seven months have 31 days: January, March, May, July, August, October, and December. You can remember this using the knuckle method or the classic rhyme "Thirty days has September..."
Business days per month vary from 19 to 23 depending on weekends and holidays. In 2026, February and November have the fewest (19 each), while March, April, July, and December have the most (22 each). The annual total is 251 business days. See our business days per year guide for details.