Let's start by using the right nomenclature with reference to the medical component of your salary.
It should be termed Medical Reimbursement, not Medical Allowance. This is because allowance per se is taxable in all cases, except those specifically exempted.
For general medical reimbursement, Rs 15,000 is the maximum tax break that an individual can avail of against actual supporting documents.
Let's say that, based on your company rules, you are eligible for medical reimbursement of a month's basic salary. Let's further assume that this is Rs 30,000.
So the amount you are eligible for reimbursement is Rs 30,000.
Now there are two aspects to this situation: you need to submit at least Rs 30,000 worth of medical bills to claim the eligible reimbursement from your employer.
Second, the tax break would only be available for Rs 15,000, though you have provided bills for Rs 30,000.
Note :
If an employee receives some money for his medical treatment or the treatment of any member of his family or any of his dependant relatives then a sum up to Rs. 15,000 p.a. is not treated as a taxable perquisite as per Clause (b) of the provision to Section 17 (2) of the I.TA. Act. This exemption is enjoyed by the employee only if the expenditure is actually incurred on his medical treatment or for treatment of any member of the family or a dependant relative. It may be noted here that there is no condition that the medical treatment should be at any of the approved hospitals. It could be at any place and from any type of doctor belonging to Allopathic, Ayurvedic, Unani or Naturopathy system of medicine. If medical allowance is received then it would be fully taxable.
In income tax act no where is mentioned the Monthly Limit.