diff --git a/firmware/targets/f7/api_symbols.csv b/firmware/targets/f7/api_symbols.csv
index fae2f10c39b..1055cb2bfd4 100644
--- a/firmware/targets/f7/api_symbols.csv
+++ b/firmware/targets/f7/api_symbols.csv
@@ -1,5 +1,5 @@
 entry,status,name,type,params
-Version,+,27.0,,
+Version,+,27.1,,
 Header,+,applications/services/bt/bt_service/bt.h,,
 Header,+,applications/services/cli/cli.h,,
 Header,+,applications/services/cli/cli_vcp.h,,
@@ -1313,6 +1313,8 @@ Function,+,furi_hal_rtc_datetime_to_timestamp,uint32_t,FuriHalRtcDateTime*
 Function,-,furi_hal_rtc_deinit_early,void,
 Function,+,furi_hal_rtc_get_boot_mode,FuriHalRtcBootMode,
 Function,+,furi_hal_rtc_get_datetime,void,FuriHalRtcDateTime*
+Function,+,furi_hal_rtc_get_days_per_month,uint8_t,"_Bool, uint8_t"
+Function,+,furi_hal_rtc_get_days_per_year,uint16_t,uint16_t
 Function,+,furi_hal_rtc_get_fault_data,uint32_t,
 Function,+,furi_hal_rtc_get_heap_track_mode,FuriHalRtcHeapTrackMode,
 Function,+,furi_hal_rtc_get_locale_dateformat,FuriHalRtcLocaleDateFormat,
@@ -1325,6 +1327,7 @@ Function,+,furi_hal_rtc_get_timestamp,uint32_t,
 Function,-,furi_hal_rtc_init,void,
 Function,-,furi_hal_rtc_init_early,void,
 Function,+,furi_hal_rtc_is_flag_set,_Bool,FuriHalRtcFlag
+Function,+,furi_hal_rtc_is_leap_year,_Bool,uint16_t
 Function,+,furi_hal_rtc_reset_flag,void,FuriHalRtcFlag
 Function,+,furi_hal_rtc_set_boot_mode,void,FuriHalRtcBootMode
 Function,+,furi_hal_rtc_set_datetime,void,FuriHalRtcDateTime*
@@ -3085,7 +3088,6 @@ Variable,+,furi_hal_i2c_bus_external,FuriHalI2cBus,
 Variable,+,furi_hal_i2c_bus_power,FuriHalI2cBus,
 Variable,+,furi_hal_i2c_handle_external,FuriHalI2cBusHandle,
 Variable,+,furi_hal_i2c_handle_power,FuriHalI2cBusHandle,
-Variable,+,furi_hal_rtc_days_per_month,const uint8_t[2][12],
 Variable,+,furi_hal_sd_spi_handle,FuriHalSpiBusHandle*,
 Variable,+,furi_hal_spi_bus_d,FuriHalSpiBus,
 Variable,+,furi_hal_spi_bus_handle_display,FuriHalSpiBusHandle,
diff --git a/firmware/targets/f7/furi_hal/furi_hal_rtc.c b/firmware/targets/f7/furi_hal/furi_hal_rtc.c
index abce7de920a..8dfe1a13ec7 100644
--- a/firmware/targets/f7/furi_hal/furi_hal_rtc.c
+++ b/firmware/targets/f7/furi_hal/furi_hal_rtc.c
@@ -39,7 +39,13 @@ typedef struct {
 
 _Static_assert(sizeof(SystemReg) == 4, "SystemReg size mismatch");
 
-const uint8_t furi_hal_rtc_days_per_month[2][FURI_HAL_RTC_MONTHS_COUNT] = {
+#define FURI_HAL_RTC_SECONDS_PER_MINUTE 60
+#define FURI_HAL_RTC_SECONDS_PER_HOUR (FURI_HAL_RTC_SECONDS_PER_MINUTE * 60)
+#define FURI_HAL_RTC_SECONDS_PER_DAY (FURI_HAL_RTC_SECONDS_PER_HOUR * 24)
+#define FURI_HAL_RTC_MONTHS_COUNT 12
+#define FURI_HAL_RTC_EPOCH_START_YEAR 1970
+
+static const uint8_t furi_hal_rtc_days_per_month[2][FURI_HAL_RTC_MONTHS_COUNT] = {
     {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31},
     {31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}};
 
@@ -387,7 +393,7 @@ uint32_t furi_hal_rtc_datetime_to_timestamp(FuriHalRtcDateTime* datetime) {
     uint8_t leap_years = 0;
 
     for(uint16_t y = FURI_HAL_RTC_EPOCH_START_YEAR; y < datetime->year; y++) {
-        if(FURI_HAL_RTC_IS_LEAP_YEAR(y)) {
+        if(furi_hal_rtc_is_leap_year(y)) {
             leap_years++;
         } else {
             years++;
@@ -398,10 +404,10 @@ uint32_t furi_hal_rtc_datetime_to_timestamp(FuriHalRtcDateTime* datetime) {
         ((years * furi_hal_rtc_days_per_year[0]) + (leap_years * furi_hal_rtc_days_per_year[1])) *
         FURI_HAL_RTC_SECONDS_PER_DAY;
 
-    uint8_t year_index = (FURI_HAL_RTC_IS_LEAP_YEAR(datetime->year)) ? 1 : 0;
+    bool leap_year = furi_hal_rtc_is_leap_year(datetime->year);
 
-    for(uint8_t m = 0; m < (datetime->month - 1); m++) {
-        timestamp += furi_hal_rtc_days_per_month[year_index][m] * FURI_HAL_RTC_SECONDS_PER_DAY;
+    for(uint8_t m = 1; m < datetime->month; m++) {
+        timestamp += furi_hal_rtc_get_days_per_month(leap_year, m) * FURI_HAL_RTC_SECONDS_PER_DAY;
     }
 
     timestamp += (datetime->day - 1) * FURI_HAL_RTC_SECONDS_PER_DAY;
@@ -411,3 +417,15 @@ uint32_t furi_hal_rtc_datetime_to_timestamp(FuriHalRtcDateTime* datetime) {
 
     return timestamp;
 }
+
+uint16_t furi_hal_rtc_get_days_per_year(uint16_t year) {
+    return furi_hal_rtc_days_per_year[furi_hal_rtc_is_leap_year(year) ? 1 : 0];
+}
+
+bool furi_hal_rtc_is_leap_year(uint16_t year) {
+    return (((year) % 4 == 0) && ((year) % 100 != 0)) || ((year) % 400 == 0);
+}
+
+uint8_t furi_hal_rtc_get_days_per_month(bool leap_year, uint8_t month) {
+    return furi_hal_rtc_days_per_month[leap_year ? 1 : 0][month - 1];
+}
diff --git a/firmware/targets/furi_hal_include/furi_hal_rtc.h b/firmware/targets/furi_hal_include/furi_hal_rtc.h
index ed7aee228dc..186d22f0798 100644
--- a/firmware/targets/furi_hal_include/furi_hal_rtc.h
+++ b/firmware/targets/furi_hal_include/furi_hal_rtc.h
@@ -12,17 +12,6 @@
 extern "C" {
 #endif
 
-#define FURI_HAL_RTC_SECONDS_PER_MINUTE 60
-#define FURI_HAL_RTC_SECONDS_PER_HOUR (FURI_HAL_RTC_SECONDS_PER_MINUTE * 60)
-#define FURI_HAL_RTC_SECONDS_PER_DAY (FURI_HAL_RTC_SECONDS_PER_HOUR * 24)
-#define FURI_HAL_RTC_EPOCH_START_YEAR 1970
-#define FURI_HAL_RTC_IS_LEAP_YEAR(year) \
-    ((((year) % 4 == 0) && ((year) % 100 != 0)) || ((year) % 400 == 0))
-
-#define FURI_HAL_RTC_MONTHS_COUNT 12
-
-extern const uint8_t furi_hal_rtc_days_per_month[2][FURI_HAL_RTC_MONTHS_COUNT];
-
 typedef struct {
     // Time
     uint8_t hour; /**< Hour in 24H format: 0-23 */
@@ -266,6 +255,30 @@ uint32_t furi_hal_rtc_get_timestamp();
  */
 uint32_t furi_hal_rtc_datetime_to_timestamp(FuriHalRtcDateTime* datetime);
 
+/** Gets the number of days in the year according to the Gregorian calendar.
+ *
+ * @param year Input year.
+ *
+ * @return number of days in `year`.
+ */
+uint16_t furi_hal_rtc_get_days_per_year(uint16_t year);
+
+/** Check if a year a leap year in the Gregorian calendar.
+ *
+ * @param year Input year.
+ *
+ * @return true if `year` is a leap year.
+ */
+bool furi_hal_rtc_is_leap_year(uint16_t year);
+
+/** Get the number of days in the month.
+ *
+ * @param leap_year true to calculate based on leap years
+ * @param month month to check, where 1 = January
+ * @return the number of days in the month
+ */
+uint8_t furi_hal_rtc_get_days_per_month(bool leap_year, uint8_t month);
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/lib/nfc/parsers/opal.c b/lib/nfc/parsers/opal.c
index 05b67fd7ec9..5a54dc82001 100644
--- a/lib/nfc/parsers/opal.c
+++ b/lib/nfc/parsers/opal.c
@@ -64,7 +64,7 @@ void opal_date_time_to_furi(uint16_t days, uint16_t minutes, FuriHalRtcDateTime*
     if(!out) return;
     uint16_t diy;
     out->year = 1980;
-    out->month = 0;
+    out->month = 1;
     // 1980-01-01 is a Tuesday
     out->weekday = ((days + 1) % 7) + 1;
     out->hour = minutes / 60;
@@ -73,7 +73,7 @@ void opal_date_time_to_furi(uint16_t days, uint16_t minutes, FuriHalRtcDateTime*
 
     // What year is it?
     for(;;) {
-        diy = (FURI_HAL_RTC_IS_LEAP_YEAR(out->year) ? 366 : 365);
+        diy = furi_hal_rtc_get_days_per_year(out->year);
         if(days < diy) break;
         days -= diy;
         out->year++;
@@ -82,16 +82,15 @@ void opal_date_time_to_furi(uint16_t days, uint16_t minutes, FuriHalRtcDateTime*
     // 1-index the day of the year
     days++;
     // What month is it?
-    uint8_t is_leap = diy - 365;
+    bool is_leap = furi_hal_rtc_is_leap_year(out->year);
 
     for(;;) {
-        uint8_t dim = furi_hal_rtc_days_per_month[is_leap][out->month];
+        uint8_t dim = furi_hal_rtc_get_days_per_month(is_leap, out->month);
         if(days <= dim) break;
         days -= dim;
         out->month++;
     }
 
-    out->month++;
     out->day = days;
 }