The top-up plan offers you an additional cover when you exhaust your basic cover limit. This can be easily understood with a simple example.
Mr. Raj has a regular /primary health insurance cover for rupees 5 lakh. He purchases a top up health insurance for rupees 5 lakh.
Case 1: A medical bill of rupees 4 lakh is made. Then the regular health insurance will pay for the bills.
Case 2: A medical bill of rupees 9 lakh is made. Then the first 5 lakh is paid by the regular health insurance and the remaining 4 lakh is paid by the top up plan.
Case 3: A medical bill of rupees 12 lakh is made. Then the first 5 lakh is paid by the regular health insurance. The top up plan pays 5 lakh and the remaining 2 lakh is paid by Mr. Raj from his pocket.
Almost every insurance company now provides the top up insurance option along with the regular health insurance. It is up to the policy holder to look at the features, terms and conditions, premium etc before buying the add on plan.