Accounting Period overlap validation
diff --git a/erpnext/accounts/doctype/accounting_period/accounting_period.py b/erpnext/accounts/doctype/accounting_period/accounting_period.py
index 030189d..306bf91 100644
--- a/erpnext/accounts/doctype/accounting_period/accounting_period.py
+++ b/erpnext/accounts/doctype/accounting_period/accounting_period.py
@@ -13,3 +13,22 @@
 	def autoname(self):
 		company_abbr = frappe.db.get_value("Company", self.company, "abbr")
 		self.name = " - ".join([self.period_name, company_abbr])
+	
+	def validate_overlap(self):
+			existing_accounting_period = frappe.db.sql("""select name from `tabAccounting Period`
+				where (
+					(%(start_date)s between start_date and end_date)
+					or (%(end_date)s between start_date and end_date)
+					or (start_date between %(start_date)s and %(end_date)s)
+					or (end_date between %(start_date)s and %(end_date)s)
+				) and name!=%(name)s and company=%(company)s""",
+				{
+					"start_date": self.start_date,
+					"end_date": self.end_date,
+					"name": self.name,
+					"company": self.company
+				}, as_dict=True)
+
+			if len(existing_accounting_period) > 0:
+				frappe.throw("Accounting Period overlaps with {0}".format(existing_accounting_period[0].get("name")))
+