What does XVIII mean in Roman numerals?



MMXVII AD = In the Year of the Lord 2017 = 2017 AD.

numbervalue
no sign0
I.1
II2
III3
IV4
V.5
VI6
VII7
VIII8
IX9
X10
XI11
XII12
XIII13
XIV14
XV15
XVI16
XVII17
XVIII18
XIX19
XX20
XXI21
XXV25
XXX30
XL40
XLIX49
L.50
LX60
LXX70
LXXX80
XC90
XCV95
XCIX99
C.100
CX110
CC200
CCC300
CD400
D.500
DC600
DCC700
DCCC800
CM900
CMXC990
CMXCIX999
M.1.000
MCMLXXXIV1.984
MM2.000
MMM3.000
Mↁ4.000
ↁ5.000
Mↂ9.000
ↂ10.000

Remarks:

N (nulla) sometimes stands for "zero" (zero).
The following notation of the numbers 49 as IL, 95 as VC, 99 as IC, 990 as XM and 999 as IM is not permitted.