diff --git a/src/date/date.h b/src/date/date.h
index e824764..9da4f93 100644
--- a/src/date/date.h
+++ b/src/date/date.h
@@ -5,7 +5,7 @@
  */
 
 /* 
- * Copyright (c) 2012-2022, Tomasz Sowa
+ * Copyright (c) 2012-2023, Tomasz Sowa
  * All rights reserved.
  * 
  * Redistribution and use in source and binary forms, with or without
@@ -60,6 +60,11 @@ class Date
 {
 public:
 
+	static const time_t ONE_MIN  = 60;              /* one minute in seconds */
+	static const time_t ONE_HOUR = ONE_MIN * 60;    /* one hour in seconds   */
+	static const time_t ONE_DAY  = ONE_HOUR * 24;   /* one day in seconds    */
+	static const time_t ONE_WEEK = ONE_DAY * 7;     /* one week in seconds   */
+
 
 	/*
 		the date