diff --git a/.gitignore b/.gitignore
index deb846a..053f511 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,5 +1,5 @@
 node_modules
-calendars
-locales
-dist
+/calendars
+/locales
+/dist
 test.js
diff --git a/index.d.ts b/index.d.ts
index d37ac05..9864af0 100644
--- a/index.d.ts
+++ b/index.d.ts
@@ -551,6 +551,14 @@ declare module "react-date-object/calendars/julian" {
   export = julian;
 }
 
+declare module "react-date-object/calendars/real-persian" {
+  import type { Calendar } from "react-date-object";
+
+  const realPersian: Omit<Calendar, "leapsLength">;
+
+  export default realPersian;
+}
+
 declare module "react-date-object/locales/gregorian_en" {
   import type { Locale } from "react-date-object";
 
diff --git a/rollup.config.js b/rollup.config.js
index ca3685f..14b6edc 100644
--- a/rollup.config.js
+++ b/rollup.config.js
@@ -41,8 +41,32 @@ export default [
   },
   ...build("calendars"),
   ...build("locales"),
+  ...buildCustom("calendars"),
 ];
 
+function buildCustom(path) {
+  const customPath = `./src/${path}`;
+
+  if (!fs.existsSync(customPath)) return [];
+
+  return fs
+    .readdirSync(customPath)
+    .filter((file) => file.endsWith(".js"))
+    .map((file) => file.replace(/\.js$/, ""))
+    .map((name) => ({
+      input: `${customPath}/${name}.js`,
+      output: [
+        {
+          file: `${path}/${name}.js`,
+          format: "cjs",
+          exports: "default",
+          plugins: [terser()],
+        },
+      ],
+      plugins: [commonjs()],
+    }));
+}
+
 function build(path) {
   const nodePath = `./node_modules/date-object/${path}`;
   const array = fs
diff --git a/src/calendars/real-persian.js b/src/calendars/real-persian.js
new file mode 100644
index 0000000..4a121cf
--- /dev/null
+++ b/src/calendars/real-persian.js
@@ -0,0 +1,50 @@
+"use strict";
+
+var persian = require("../../node_modules/date-object/calendars/cjs/persian");
+
+// The "Old Persian" (Imperial/Shahanshahi) calendar uses the same
+// solar calendar as the modern Persian (Solar Hijri) calendar,
+// but counts years from the founding of the Achaemenid Empire
+// by Cyrus the Great (559 BCE) instead of the Islamic Hijra (622 CE).
+
+var HIJRI_EPOCH_CE = 622;
+var ACHAEMENID_EPOCH_BCE = 559;
+var YEAR_OFFSET = HIJRI_EPOCH_CE + ACHAEMENID_EPOCH_BCE - 1; // 1180
+
+var realPersian = {
+  name: "real-persian",
+  startYear: persian.startYear + YEAR_OFFSET,
+  yearLength: persian.yearLength,
+  epoch: persian.epoch,
+  century: Math.ceil((persian.century * 100 + YEAR_OFFSET) / 100),
+  weekStartDayIndex: persian.weekStartDayIndex,
+  getMonthLengths: function (isLeap) {
+    return persian.getMonthLengths(isLeap);
+  },
+  isLeap: function (year) {
+    return persian.isLeap(year - YEAR_OFFSET);
+  },
+  getLeaps: function (currentYear) {
+    var persianYear = currentYear - YEAR_OFFSET;
+    var leaps = persian.getLeaps(persianYear);
+    if (!leaps) return leaps;
+    return leaps.map(function (y) {
+      return y + YEAR_OFFSET;
+    });
+  },
+  getDayOfYear: function (date) {
+    return persian.getDayOfYear(date);
+  },
+  getAllDays: function (date) {
+    return persian.getAllDays.call(persian, {
+      year: date.year - YEAR_OFFSET,
+      month: date.month,
+      day: date.day,
+    });
+  },
+  guessYear: function (days, currentYear) {
+    return persian.guessYear(days, currentYear) + YEAR_OFFSET;
+  },
+};
+
+module.exports = realPersian;