Madam Niki Liu never realised how much her Integrated Shield Plan (IP) was costing her until this year.
After doing the sums, the 45-year-old discovered that her Medisave account - which she had been drawing on to pay the premiums - would run dry in about 10 years.
"I used to work, so at that time I didn't do the calculations," said the former bank teller. She stopped work when her youngest child, Rey Phua, was born six years ago.
Madam Liu started working out the sums only when her insurer told her her premium would go up to more than $600 a year - an increase of about $200.
"Ten to 12 years down the road, I won't have enough," said the mother of three.
Her husband, the family's sole breadwinner, earns about $1,800 a month.
IPs started in 2005 as an add-on to the basic MediShield.
Offered by companies such as Aviva and Prudential, they give policyholders extra benefits such as coverage for private hospital stays.
Around two-thirds of those insured under MediShield are on such plans. But, like Madam Liu, not everyone realises how pricey IPs can get over a lifetime.
"A lot of them now realise they cannot sustain this when they are retiring, when suddenly the premiums shoot up," said health economist Phua Kai Hong of the Lee Kuan Yew School of Public Policy.
He pointed out that IPs became popular as MediShield did not provide adequate coverage for big hospital bills.
But he expects many policyholders to terminate their private plans once MediShield Life, with its better terms, kicks in next year.
More details about how IPs will work with MediShield Life are set to be released at the end of this month.
Dr Chia Shi-Lu, head of the Government Parliamentary Committee for Health, added that anyone in Madam Liu's shoes should consider carefully before opting for IPs, especially if they do not intend to make use of the additional frills.
"These are nice to have, but not essential as the overall quality of care itself would be similar in restructured hospitals," he said.
And since the news of her premium increase, Madam Liu has been thinking twice about maintaining her private plan.
She has already decided to opt for a Class C ward in the event of her hospitalisation.
"I wouldn't want to drain the family, just because I'm lying down in a bed," she said.