Is it too late to paint the outside of your house this year?

The short answer

It depends far more on how far north you are than on the calendar. Across 3,206 places, 1,790 (56%) still have a good painting month in September, 945 (29%) in October and only 348 (11%) in November. For 1,357 places the last good month of the year is September, for 380 it is August, and for 661 it is October.

When the window closes, by latitude

Latitude	Places	Typical last good month	October still good
south of 32°N (Gulf Coast, south Texas, Florida, desert Southwest)	391	November	84%
32°N to 37°N	890	October	57%
37°N to 41°N	859	September	10%
41°N to 45°N	853	September	3%
north of 45°N	213	August	0%

"Typical last good month" is the median, across the band, of the last month in the year with 12 or more painting days.

Large places where November still works

Place	Last good month	Sep days	Oct days	Nov days
Tampa, FL	December	3	15	22
Cape Coral, FL	December	2	15	21
Mesa, AZ	November	2	15	20
St. Petersburg, FL	November	6	19	20
Irvine, CA	November	24	25	20
Santa Ana, CA	November	24	25	20

Large places where it is over by October

Place	Last good month	Sep days	Oct days	Nov days
New York, NY	September	18	11	3
Chicago, IL	September	27	11	2
Philadelphia, PA	September	16	7	1
Charlotte, NC	September	14	10	2
Columbus, OH	September	15	6	1
Indianapolis, IN	September	17	6	1

Cold nights end the season, not cold days: a sunny 60°F October afternoon after a 40°F night is not a painting day for standard latex, because the film cannot cure while the wall is that cold. If you are past your window, the two honest options are low-temperature paint, which only needs a 35°F low, or booking now for the first good month next year.