Time Calculator
You can "add" or "subtract" two time values with this calculator. If you are looking to add or subtract some time from a date, please use the date calculator. Please provide the values in the fields above the "=". Then click the "Calculate" button to calculate. When entering, you can leave some fields blank. These fields will be taken as 0 by default.

Reference
Like numbers, time can be added or subtracted. However due to the definitions, time can not be simply added or subtracted like normal decimal numbers. The following are the definitions of the common time units.
Unit  Definition 
millennium  1,000 years 
century  100 years 
decade  10 years 
year (average)  365.242 days or 12 months 
common year  365 days or 12 months 
leap year  366 days or 12 months 
quarter  3 months 
month  2831 days Jan., Mar., May, Jul., Aug. Oct., Dec.—31 days Apr., Jun., Sep., Nov.—30 days. Feb.—28 days for common year and 29 days for leap year 
week  7 days 
day  24 hours or 1,440 minutes or 86,400 seconds 
hour  60 minutes or 3,600 seconds 
minute  60 seconds 
second  base unit 
millisecond  10^{3} second 
microsecond  10^{6} second 
nanosecond  10^{9} second 
picosecond  10^{12} second 