Found an entry on this page saying Classical Period concert music ran from 1750 to 1850. Have checked several sources online for this, and none list 1850 as the end point; am listing them with links.
Brittanica: Says "The Classical era in music is compositionally defined by the balanced eclecticism of the late 18th- and early 19th-century Viennese “school” of Haydn, Mozart, Beethoven, and Schubert, who completely absorbed and individually fused or transformed the vast array of 18th-century textures and formal types." Haydn's career has the earliest start, first pieces written in 1756. Schubert's career extended the latest, last pieces written in 1828.
Link: https://www.britannica.com/art/musical-composition/The-Classical-period
String Ovation: says "However, the Classical Era is often cited as the latter half of the eighteenth century. At its longest, the Classical Era ran just seventy to eighty years, ending no later than 1820." The starting point would be sometime between 1740 and 1750.
Link: https://www.connollymusic.com/stringovation/the-classical-period-of-music
Found an entry on this page saying Classical Period concert music ran from 1750 to 1850. Have checked several sources online for this, and none list 1850 as the end point; am listing them with links.
Wikipedia: 1750-1820 Link: https://en.wikipedia.org/wiki/Classical_period_(music)
Classic FM: 1750-1830 Link: https://www.classicfm.com/discover-music/four-eras-classical-music/
Masterclass.com: 1730-1820 Link: https://www.masterclass.com/articles/classical-era-music-guide
Brittanica: Says "The Classical era in music is compositionally defined by the balanced eclecticism of the late 18th- and early 19th-century Viennese “school” of Haydn, Mozart, Beethoven, and Schubert, who completely absorbed and individually fused or transformed the vast array of 18th-century textures and formal types." Haydn's career has the earliest start, first pieces written in 1756. Schubert's career extended the latest, last pieces written in 1828. Link: https://www.britannica.com/art/musical-composition/The-Classical-period
String Ovation: says "However, the Classical Era is often cited as the latter half of the eighteenth century. At its longest, the Classical Era ran just seventy to eighty years, ending no later than 1820." The starting point would be sometime between 1740 and 1750. Link: https://www.connollymusic.com/stringovation/the-classical-period-of-music
Skoove: 1750-1820. Link: https://www.skoove.com/blog/classical-music-eras/
Lumen Learning: 1750-1820. Link: https://courses.lumenlearning.com/suny-musicapp-medieval-modern/chapter/the-classical-era/
Hello Music Theory.com: 1730-1820. Link: https://hellomusictheory.com/learn/classical-music-eras/
Virtual Music Classroom: 1750-1820. Link: https://virtualmusicclassroom08416826.wordpress.com/classical-period-1750-1820/
Given all this, I've changed the period's dates from 1750-1850 to 1750-1820, the latter seeming to be the best compromise choice.