diff --git a/src/Makefile b/src/Makefile
index 4101235..409a03a 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -51,7 +51,7 @@ HACKERBASE-OBJS=hackerbase.o testing.o listing.o cal-month.o		\
 	 util-string.o util-io.o util-list.o util-parser.o texts.o	\
 	 tests.o util-proc.o util-mail.o notifications.o		\
 	 util-format.o brmember-format.o logging.o specification.o	\
-	 util-git.o cal-day.o util-stdout.o
+	 util-git.o cal-day.o util-stdout.o cal-format.o
 
 .PHONY: imports
 imports: $(HACKERBASE-DEPS)
@@ -379,3 +379,8 @@ UTIL-STDOUT-SOURCES=util-stdout.scm
 
 util-stdout.o: util-stdout.import.scm
 util-stdout.import.scm: $(UTIL-STDOUT-SOURCES)
+
+CAL-FORMAT-SOURCES=cal-format.scm cal-day.import.scm cal-month.import.scm
+
+cal-format.o: cal-format.import.scm
+cal-format.import.scm: $(CAL-FORMAT-SOURCES)
diff --git a/src/cal-format.scm b/src/cal-format.scm
new file mode 100644
index 0000000..d6bd652
--- /dev/null
+++ b/src/cal-format.scm
@@ -0,0 +1,46 @@
+;;
+;; cal-format.scm
+;;
+;; Calendar structures formatting.
+;;
+;; ISC License
+;;
+;; Copyright 2023 Brmlab, z.s.
+;; Dominik Pantůček <dominik.pantucek@trustica.cz>
+;;
+;; Permission to use, copy, modify, and/or distribute this software
+;; for any purpose with or without fee is hereby granted, provided
+;; that the above copyright notice and this permission notice appear
+;; in all copies.
+;; 
+;; THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL
+;; WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED
+;; WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE
+;; AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR
+;; CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS
+;; OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT,
+;; NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
+;; CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+;;
+
+(declare (unit cal-format))
+
+(module
+ cal-format
+ (
+  cal-format
+  )
+
+ (import scheme
+	 cal-day
+	 cal-month)
+
+ ;; Formats day or month or #f to string.
+ (define (cal-format v)
+   (if (cal-day? v)
+       (cal-day->string v)
+       (if (cal-month? v)
+	   (cal-month->string v)
+	   "--")))
+
+ )