This page shows various possible month lengths for calendars with a particular number of months in a year as shown in table of contents.
12 months [ ]
Systematic month lengths in 12-month calendars
Year
Half
Third
Quarter
Sixth
Month
Irregular
61-day double-month
91-day quarter
30-day month
Greg/Jul
common
31:30
30:31
31:30*
30:31*
common
31:30:30
30:31:30
30:30:31
5:4:4
4:5:4
4:4:5
Y
H1
T1
Q1
S1
M01
365⁺
181⁺
120⁺
90⁺
59⁺
31
366⁻
183
122
61
92
31
91
30
92
31
91
30
364⁺
182
91
122
61
31
121
61
30
121
60
30
126
63
35
119
63
28
119
56
28
360⁺
180
120
90
60
30
M02
28⁺
30
31
30
31
30
31
30
28
35
28
30
S2
M03
61
31
61
31
30
31
30
61
30
60
30
61
31
63
28
56
28
63
35
60
30
Q2
M04
91
30
91
30
92
31
91
30
92
31
91
31
30
30
35
28
28
90
30
T2
S3
M05
123
61
31
122
61
31
30
31
30
121
60
30
122
61
31
121
61
30
119
56
28
126
63
35
119
63
28
120
60
30
M06
30
30
31
30
31
30
30
31
28
28
35
30
H2
Q3
S4
M07
184
92
62
31
183
61
92
31
91
30
91
30
92
31
182
91
61
31
61
30
60
30
63
35
63
28
56
28
180
90
60
30
M08
31
30
31
31
30
30
31
30
28
35
28
30
T3
S5
M09
122
61
30
122
61
31
30
30
31
121
61
30
121
60
30
122
61
31
119
63
28
119
56
28
126
63
35
120
60
30
Q4
M10
92
31
91
30
92
31
92
31
91
30
91
31
30
30
35
28
28
90
30
S6
M11
61
30
61
31
30
30
31
60
30
61
31
61
30
56
28
63
35
63
28
60
30
M12
31
30
31
31
30
30
30
31
28
28
35
30
Ordinal start dates in 12-month calendars
Year
Half
Third
Quarter
Sixth
Month
Irregular
61-day double-month
91-day quarter
Constant
Greg/Jul
31:30
30:31
31:30*
30:31*
31:30:30
30:31:30
30:30:31
5:4:4
4:5:4
4:4:5
30
Y
H1
T1
Q1
S1
M01
001
001
001
001
001
001
001
001
001
001
001
001
M02
032
032
031
032
031
032
031
031
036
029
029
031
S2
M03
060+
062
062
062
062
062
062
061
064
064
057
061
Q2
M04
091+
093
092
093
092
092
092
092
092
092
092
091
T2
S3
M05
121+
123
123
123
123
123
122
122
127
120
120
121
M06
152+
154
153
154
153
153
153
152
155
155
148
151
H2
Q3
S4
M07
182+
184
184
184
184
183
183
183
183
183
183
181
M08
213+
215
214
214
215
214
213
213
218
211
211
211
T3
S5
M09
244+
245
245
245
245
244
244
243
246
246
239
241
Q4
M10
274+
276
275
275
276
274
274
274
274
274
274
271
S6
M11
305+
306
306
306
306
305
304
304
309
302
302
301
M12
335+
337
336
336
337
335
335
334
337
337
330
331
Comparison to legacy months in common years of 12-month calendars
Difference
61-day double-month
91-day quarter
Constant
31:30
30:31
31:30*
30:31*
31:30:30
30:31:30
30:30:31
5:4:4
4:5:4
4:4:5
30
length
+3…+7
–
1
–
1
–
1
–
4
4
4
–
+2
1
–
1
–
1
–
1
–
–
–
1
+1
2
2
–
4
1
1
2
–
–
–
–
±0
6
5
10
1
6
5
4
1
0
1
4
−1
3
4
1
6
4
5
5
–
–
–
7
−2…−3
–
–
–
–
–
–
–
7
8
7
–
offsets
+3…+6
–
–
–
–
–
–
–
6
2
–
–
+2
8
3
5
6
2
1
–
2
2
–
–
+1
2
7
5
4
4
4
4
2
2
2
1
±0
2
1
2
1
6
5
4
2
2
2
3
−1
–
1
–
1
–
2
4
–
1
1
3
−2…−5
–
–
–
–
–
–
–
–
3
7
5
13 months [ ]
Systematic month lengths in 13-month calendars
Year
Month
4-week
Y
M01
364⁺
28
M02
28
M03
28
M04
28
M05
28
M06
28
M07
28
M08
28
M09
28
M10
28
M11
28
M12
28
M13
28
14 months [ ]
Systematic lengths in 14-month calendars
Year
Half
Seventh
Month
common
(regular)
4-week
26
3–4
3–4*
4–3
4–3*
Y
H1
S1
M01
364⁺
182
52
26
56
28
56
28
56
28
56
28
M02
26
28
28
28
28
S2
M03
52
26
49
21
49
28
49
28
49
21
M04
26
28
21
21
28
S3
M05
52
26
56
28
56
28
56
28
56
28
M06
26
28
28
28
28
S4
M07
52
26
49
21
49
21
49
21
49
21
H2
M08
182
26
28
28
28
28
S5
M09
52
26
49
28
49
28
56
28
56
28
M10
26
21
28
28
28
S6
M11
52
26
56
28
56
28
49
21
49
21
M12
26
28
28
28
28
S7
M13
52
26
49
28
49
28
49
28
49
28
M14
26
21
21
21
21
10 months [ ]
Systematic lengths in 10-month calendars
Year
Half
Fifth
Month
(alternating)
(constant)
5-week
common
36:37
37:36
36⁺
common
1st
2nd
3rd
4th
5th
Y
H1
F1
M01
365⁺
73
182
36
183
37
360⁺
180
72
36
364⁺
182
77
42
77
35
70
35
70
35
70
35
M02
37
36
36
35
42
35
35
35
F2
M03
73
36
37
72
36
70
35
70
35
77
42
77
35
70
35
M04
37
36
36
35
35
35
42
35
F3
M05
73
36
37
72
36
77
35
70
35
70
35
70
35
77
42
H2
M06
183
37
182
36
180
36
182
42
35
35
35
35
F4
M07
73
36
37
72
36
70
35
77
42
77
35
70
35
70
35
M08
37
36
36
35
35
42
35
35
F5
M09
73
36
37
72
36
70
35
70
35
70
35
77
42
77
35
M10
37
36
36
35
35
35
35
42
11 months [ ]
Systematic month lengths in 11-month calendars
Year
Month
equal
2 longer
33
leap month
3–4–4
4–3–4
4–4–3
Y
M01
363⁺
33
350 (385)
35
365⁺
33
33
33
M02
33
35
33
33
33
M03
33
35
33
33
33
M04
33
35
33
34
34
M05
33
35
33
33
33
M06
33
35
33
33
33
M07
33
35
34
33
33
M08
33
35
33
33
34
M09
33
35
33
33
33
M10
33
35
33
33
33
M11
33
(35)
34
34
33
10+1 months [ ]
A calendar with ten regular and one leap month , where each month has exactly five weeks of seven days, has years either 350 or 385 days long. This can only be compatible with leap cycles that have a number of days divisible by five, i.e. not the popular 293 and 400-year cycles (146097 and 107016 days respectively).