diff --git a/sys/include/bcd.h b/sys/include/bcd.h
new file mode 100644
index 0000000000..67b65f3a0a
--- /dev/null
+++ b/sys/include/bcd.h
@@ -0,0 +1,60 @@
+/*
+ * Copyright (C) 2017 Freie Universität Berlin
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser
+ * General Public License v2.1. See the file LICENSE in the top level
+ * directory for more details.
+ */
+
+/**
+ * @defgroup    sys_bcd Binary coded decimal
+ * @ingroup     sys
+ * @brief       Library to de- and encode binary coded decimals
+ * @{
+ *
+ * @file
+ * @brief       BCD definitions
+ *
+ * @author  Martine Lenders <m.lenders@fu-berlin.de>
+ */
+#ifndef BCD_H
+#define BCD_H
+
+#include <stdint.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * @brief   Converts a byte to a binary coded decimal
+ *
+ * @param[in] byte  A byte
+ *
+ * @return  A binary coded decimal (4 MSB = 10s, 4 LSB = 1s)
+ */
+static inline uint8_t bcd_from_byte(uint8_t byte)
+{
+    /* ((byte / 10) << 4) | (byte % 10) */
+    return byte + (6 * (byte / 10));
+}
+
+/**
+ * @brief   Converts a binary coded decimal to a byte
+ *
+ * @param[in] bcd   A binary coded decimal (4 MSB = 10, 4 LSB = 1s)
+ *
+ * @return  A byte
+ */
+static inline uint8_t bcd_to_byte(uint8_t bcd)
+{
+    /* == (10 * (bcd >> 4)) + (bcd & 0xf) */
+    return bcd - (6 * (bcd >> 4));
+}
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* BCD_H */
+/** @} */