diff --git a/src/cal-period.scm b/src/cal-period.scm
index bfe492d..fd3c071 100644
--- a/src/cal-period.scm
+++ b/src/cal-period.scm
@@ -44,6 +44,9 @@
   
   cal-month-in-period?
   cal-month-in-periods?
+
+  cal-day-in-period?
+  cal-day-in-periods?
   
   cal-periods->string
   cal-periods-match
@@ -227,6 +230,18 @@
 	      (cal-day<? d before))
 	  (not (cal-day<? d since)))))
 
+ ;; Returns true if the day belongs to at least one period
+ (define (cal-day-in-periods? ps . dl)
+   (let ((d (if (null? dl)
+		(*current-day*)
+		(cal-ensure-day (car dl)))))
+     (let loop ((ps ps))
+       (if (null? ps)
+	   #f
+	   (if (cal-day-in-period? (car ps) d)
+	       #t
+	       (loop (cdr ps)))))))
+
  ;; Returns string representing a month period with possibly open end.
  (define (cal-period->string p)
    (sprintf "~A..~A"