diff --git a/erpnext/payroll/doctype/salary_slip/salary_slip.py b/erpnext/payroll/doctype/salary_slip/salary_slip.py
index b035292..a4e75ac 100644
--- a/erpnext/payroll/doctype/salary_slip/salary_slip.py
+++ b/erpnext/payroll/doctype/salary_slip/salary_slip.py
@@ -932,8 +932,11 @@
 	def get_future_recurring_additional_amount(self, additional_salary, monthly_additional_amount):
 		future_recurring_additional_amount = 0
 		to_date = frappe.db.get_value("Additional Salary", additional_salary, 'to_date')
+
 		# future month count excluding current
-		future_recurring_period = (getdate(to_date).month - getdate(self.start_date).month)
+		from_date, to_date = getdate(self.start_date), getdate(to_date)
+		future_recurring_period = ((to_date.year - from_date.year) * 12) + (to_date.month - from_date.month)
+
 		if future_recurring_period > 0:
 			future_recurring_additional_amount = monthly_additional_amount * future_recurring_period # Used earning.additional_amount to consider the amount for the full month
 		return future_recurring_additional_amount
@@ -1032,7 +1035,8 @@
 		data.update({"annual_taxable_earning": annual_taxable_earning})
 		tax_amount = 0
 		for slab in tax_slab.slabs:
-			if slab.condition and not self.eval_tax_slab_condition(slab.condition, data):
+			cond = cstr(slab.condition).strip()
+			if cond and not self.eval_tax_slab_condition(cond, data):
 				continue
 			if not slab.to_amount and annual_taxable_earning >= slab.from_amount:
 				tax_amount += (annual_taxable_earning - slab.from_amount + 1) * slab.percent_deduction *.01