If you are making a cash top-up to a recipient eligible for the Matched MediSave Scheme (MMSS), your cash top-up of $1,000 will first enable your recipient to enjoy the matching grant of up to $1,000 per year from the Government and will thus not be eligible for tax relief. You can continue to enjoy tax relief of up to $16,000 a year for your cash top-ups that do not attract the MMSS matching grant and the Matched Retirement Savings Scheme (MRSS) matching grant ($8,000 per year for top-ups to yourself and another $8,000 per year for top-ups to your loved ones).
For example, if you make a cash top-up of $3,000 to your MMSS-eligible loved one (and made no other top ups), your loved one will first enjoy a matching grant of $1,000 from the Government, and you will be eligible for $2,000 of tax relief on your cash top-up that did not attract the matching grant.
For more information on the conditions for tax relief, you may refer to this
FAQ.