1645 (MDCXLV) was a common year starting on Sunday of the Gregorian calendar and a common year starting on Wednesday of the Julian calendar, the 1645th year of the Common Era (CE) and Anno Domini (AD) designations, the 645th year of the 2nd millennium, the 45th year of the 17th century, and the 6th year of the 1640s decade. As of the start of 1645, the Gregorian calendar was 10 days ahead of the Julian calendar, which remained in localized use until 1923.

Millennium: 2nd millennium
Centuries: 16th century17th century18th century
Decades: 1610s  1620s  1630s  – 1640s –  1650s  1660s  1670s
Years: 1642 1643 164416451646 1647 1648
1645 in other calendars
Gregorian calendar1645
Ab urbe condita2398
Armenian calendar1094
Assyrian calendar6395
Balinese saka calendar1566–1567
Bengali calendar1052
Berber calendar2595
English Regnal year20 Cha. 1 – 21 Cha. 1
Buddhist calendar2189
Burmese calendar1007
Byzantine calendar7153–7154
Chinese calendar甲申(Wood Monkey)
4341 or 4281
    — to —
乙酉年 (Wood Rooster)
4342 or 4282
Coptic calendar1361–1362
Discordian calendar2811
Ethiopian calendar1637–1638
Hebrew calendar5405–5406
Hindu calendars
 - Vikram Samvat1701–1702
 - Shaka Samvat1566–1567
 - Kali Yuga4745–4746
Holocene calendar11645
Igbo calendar645–646
Iranian calendar1023–1024
Islamic calendar1054–1055
Japanese calendarShōhō 2
Javanese calendar1566–1567
Julian calendarGregorian minus 10 days
Korean calendar3978
Minguo calendar267 before ROC
Nanakshahi calendar177
Thai solar calendar2187–2188
Tibetan calendar阳木猴年
(male Wood-Monkey)
1771 or 1390 or 618
    — to —
(female Wood-Rooster)
1772 or 1391 or 619