cljs-time gives us option to add/subtract date-times to other date-times. The date times added subtracted should be in form of days, months, years, hours etc.

(require '[clj-time.core :as t])

(def example-date (t/date-time 2016 1 1)) ;; #<DateTime 2016-01-01T00:00:00.000Z>

;; Addition
(t/plus example-date (t/months 1))        ;; #<DateTime 2016-02-01T00:00:00.000Z>
(t/plus example-date (t/years 1))         ;; #<DateTime 2017-01-01T00:00:00.000Z>

;; Subtraction
(t/minus example-date (t/days 1))          ;; #<DateTime 2015-12-31T00:00:00.000Z>
(t/minus example-date (t/hours 12))        ;; #<DateTime 2015-12-31T12:00:00.000Z>