400*13 months in 400 years
497 extra days in 400 years so
400*13/497 = xdi = 10.46277665996 months between extra days
minimum change of ofs to guarantee change of:
xdi/400  = 0.02616 one leap year
xdi/5200 = 0.00201 one extra day - with possible leap year change also
Use:
?ofs=0.06438 offset of first 'raw' extra day
&lyl for leap year list only or &both
Critical points (red circles below):
2098-12.98590 leap year
2358-01.99999 extra day
next point
next point
January
February
March
April
May
June
July
August
Hexember
September
October
November
December
January
February
March
April
May
June
July
August
Hexember
September
October
November
December
2000 5
2001
2002
2003
2004 4
2005
2006
2007
2008 4
2009
2010
2011
2012 4
2013
2014
2015
2016 4
2017
2018
2019
2020 4
2021
2022
2023
2024 4
2025
2026
2027
2028 4
2029
2030
2031
2032
2033 5
2034
2035
2036
2037 4
2038
2039
2040
2041 4
2042
2043
2044
2045 4
2046
2047
2048
2049 4
2050
2051
2052
2053 4
2054
2055
2056
2057 4
2058
2059
2060
2061 4
2062
2063
2064
2065
2066 5
2067
2068
2069
2070 4
2071
2072
2073
2074 4
2075
2076
2077
2078 4
2079
2080
2081
2082 4
2083
2084
2085
2086 4
2087
2088
2089
2090 4
2091
2092
2093
2094 4
2095
2096
2097
2098 4*
2099
2100
2101
2102
2103 5
2104
2105
2106
2107 4
2108
2109
2110
2111 4
2112
2113
2114
2115 4
2116
2117
2118
2119 4
2120
2121
2122
2123 4
2124
2125
2126
2127 4
2128
2129
2130
2131 4
2132
2133
2134
2135
2136 5
2137
2138
2139
2140 4
2141
2142
2143
2144 4
2145
2146
2147
2148 4
2149
2150
2151
2152 4
2153
2154
2155
2156 4
2157
2158
2159
2160 4
2161
2162
2163
2164 4
2165
2166
2167
2168
2169 5
2170
2171
2172
2173 4
2174
2175
2176
2177 4
2178
2179
2180
2181 4
2182
2183
2184
2185 4
2186
2187
2188
2189 4
2190
2191
2192
2193 4
2194
2195
2196
2197 4
2198
2199
2200
2201
2202 5
2203
2204
2205
2206 4
2207
2208
2209
2210 4
2211
2212
2213
2214 4
2215
2216
2217
2218 4
2219
2220
2221
2222 4
2223
2224
2225
2226 4
2227
2228
2229
2230 4
2231
2232
2233
2234
2235 5
2236
2237
2238
2239 4
2240
2241
2242
2243 4
2244
2245
2246
2247 4
2248
2249
2250
2251 4
2252
2253
2254
2255 4
2256
2257
2258
2259 4
2260
2261
2262
2263 4
2264
2265
2266
2267
2268 5
2269
2270
2271
2272 4
2273
2274
2275
2276 4
2277
2278
2279
2280 4
2281
2282
2283
2284 4
2285
2286
2287
2288 4
2289
2290
2291
2292 4
2293
2294
2295
2296 4
2297
2298
2299
2300
2301 5
2302
2303
2304
2305 4
2306
2307
2308
2309 4
2310
2311
2312
2313 4
2314
2315
2316
2317 4
2318
2319
2320
2321 4
2322
2323
2324
2325 4
2326
2327
2328
2329 4
2330
2331
2332
2333
2334 5
2335
2336
2337
2338 4
2339
2340
2341
2342 4
2343
2344
2345
2346 4
2347
2348
2349
2350 4
2351
2352
2353
2354 4
2355
2356
2357
2358 4
2359
2360
2361
2362 4
2363
2364
2365
2366
2367 5
2368
2369
2370
2371 4
2372
2373
2374
2375 4
2376
2377
2378
2379 4
2380
2381
2382
2383 4
2384
2385
2386
2387 4
2388
2389
2390
2391 4
2392
2393
2394
2395 4
2396
2397
2398
2399
2400 5
2000 5
2001
2002
2003
2004 4
2005
2006
2007
2008 4
2009
2010
2011
2012 4
2013
2014
2015
2016 4
2017
2018
2019
2020 4
2021
2022
2023
2024 4
2025
2026
2027
2028 4
2029
2030
2031
2032
2033 5
2034
2035
2036
2037 4
2038
2039
2040
2041 4
2042
2043
2044
2045 4
2046
2047
2048
2049 4
2050
2051
2052
2053 4
2054
2055
2056
2057 4
2058
2059
2060
2061 4
2062
2063
2064
2065
2066 5
2067
2068
2069
2070 4
2071
2072
2073
2074 4
2075
2076
2077
2078 4
2079
2080
2081
2082 4
2083
2084
2085
2086 4
2087
2088
2089
2090 4
2091
2092
2093
2094 4
2095
2096
2097
2098 4*
2099
2100
2101
2102
2103 5
2104
2105
2106
2107 4
2108
2109
2110
2111 4
2112
2113
2114
2115 4
2116
2117
2118
2119 4
2120
2121
2122
2123 4
2124
2125
2126
2127 4
2128
2129
2130
2131 4
2132
2133
2134
2135
2136 5
2137
2138
2139
2140 4
2141
2142
2143
2144 4
2145
2146
2147
2148 4
2149
2150
2151
2152 4
2153
2154
2155
2156 4
2157
2158
2159
2160 4
2161
2162
2163
2164 4
2165
2166
2167
2168
2169 5
2170
2171
2172
2173 4
2174
2175
2176
2177 4
2178
2179
2180
2181 4
2182
2183
2184
2185 4
2186
2187
2188
2189 4
2190
2191
2192
2193 4
2194
2195
2196
2197 4
2198
2199
2200
2201
2202 5
2203
2204
2205
2206 4
2207
2208
2209
2210 4
2211
2212
2213
2214 4
2215
2216
2217
2218 4
2219
2220
2221
2222 4
2223
2224
2225
2226 4
2227
2228
2229
2230 4
2231
2232
2233
2234
2235 5
2236
2237
2238
2239 4
2240
2241
2242
2243 4
2244
2245
2246
2247 4
2248
2249
2250
2251 4
2252
2253
2254
2255 4
2256
2257
2258
2259 4
2260
2261
2262
2263 4
2264
2265
2266
2267
2268 5
2269
2270
2271
2272 4
2273
2274
2275
2276 4
2277
2278
2279
2280 4
2281
2282
2283
2284 4
2285
2286
2287
2288 4
2289
2290
2291
2292 4
2293
2294
2295
2296 4
2297
2298
2299
2300
2301 5
2302
2303
2304
2305 4
2306
2307
2308
2309 4
2310
2311
2312
2313 4
2314
2315
2316
2317 4
2318
2319
2320
2321 4
2322
2323
2324
2325 4
2326
2327
2328
2329 4
2330
2331
2332
2333
2334 5
2335
2336
2337
2338 4
2339
2340
2341
2342 4
2343
2344
2345
2346 4
2347
2348
2349
2350 4
2351
2352
2353
2354 4
2355
2356
2357
2358 4
2359
2360
2361
2362 4
2363
2364
2365
2366
2367 5
2368
2369
2370
2371 4
2372
2373
2374
2375 4
2376
2377
2378
2379 4
2380
2381
2382
2383 4
2384
2385
2386
2387 4
2388
2389
2390
2391 4
2392
2393
2394
2395 4
2396
2397
2398
2399
2400 5
Short, thin vertical bars mark "raw" extra days spaced exactly xdi (see above) months apart.
Each of these is followed by the actual extra day in black at the end of the month in question.
The full height vertical bar is xdi months from the start of the year.
If there is a raw month marked later than this then the year will be a leap year.
The red circles, which may coincide, are critical points (see above).
As ofs is increased these are the points where a change will occur next.
php file date: 2022 Apr 26 15:04:33