diff --git a/API.md b/API.md
index 439b7fd..b034932 100644
--- a/API.md
+++ b/API.md
@@ -66,6 +66,13 @@ Returns 4 values: days, months, years and days in year (in that order)
              if `false`, use cardinal numbers
              default: false
 
+### `calendar.get_total_days_from_date(days, months, years, is_ordinal)`
+Given a date, returns the total number of elapsed days (cardinal number).
+
+* `days`/`months`/`years`: Date
+* `is_ordinal`: If `true`, date is interpreted as ordinal numbers, otherwise
+                it is interpreted as cardinal numbers (default: `false`)
+
 ## `calendar.get_weekday(total_days)`
 Returns cardinal weekday number for given day.
 
diff --git a/init.lua b/init.lua
index 697b615..f5ac17e 100644
--- a/init.lua
+++ b/init.lua
@@ -143,6 +143,15 @@ calendar.get_date = function(total_days, ordinal)
 	return d, m, y, j
 end
 
+calendar.get_total_days_from_date = function(days, months, years, is_ordinal)
+	if is_ordinal then
+		days = days - 1
+		months = months - 1
+		years = years - 1
+	end
+	return years * calendar.YEAR_DAYS + months * calendar.MONTH_DAYS + days
+end
+
 calendar.get_date_string = function(format, total_days)
 	if not total_days then
 		total_days = minetest.get_day_count()