The Prime Minister has come under fire as the winter crisis has seen delays to admissions and tens of thousands of operations being cancelled amid unprecedented pressure on hospitals.
Health service bosses have said the NHS is at "bursting point".
But Mrs May said there were winter pressures "every year", adding: "The NHS has actually been better prepared for this [sic] winter pressures than it ever has been before."
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On the subject of the delays to NHS services, the PM told the BBC’s Andrew Marr Show cancelling operations was "part of the plan".
"Of course we want to ensure that those operations can be reinstated as soon as possible, but it’s about making sure that those who most urgently need care are able to get that treatment when they need it," she said.
Mrs May was challenged about the case of Leah Butler-Smith, who waited more than four hours in an ambulance with her mother - who had suffered a stroke - at Broomfield Hospital in Essex.
She said she said that "of course nothing's perfect and there is more for us to do".
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"We have planned for the winter pressures this year," she continued.
"We did put some more money in and there has been planning and hospitals have been dealing with it in different ways."
Mrs May would not be drawn on the future funding of the NHS, after Health Secretary Jeremy Hunt suggested a 10-year funding plan.
Labour's Jonathan Ashworth told the same programme: "She hasn't got a plan to get those people off the trolleys and corridors."
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He added: "Her only plan apparently is to promote this Health Secretary. They should be demoting this Health Secretary.
He said that if the PM were to promote Mr Hunt during a Cabinet reshuffle expected in coming days, it would be "a betrayal of those 75,000 people in the back of ambulances".
Figures released earlier this week revealed almost 17,000 patients waited more than 30 minutes in ambulances at accident and emergency departments in England during the week up to New Year's Eve - up 42% from 11,900 in the previous week.
NHS England figures showed the bed occupancy rate in hospitals reached 91.7% during the festive period - 85% is considered safe.
Increased pressures on front-line services were mirrored in the NHS 111 service, which received a record 480,400 calls - up 21% from 396,300 in the previous week.
Chief executive of the Royal College of Nursing (RCN) Janet Davies said the figures showed "that almost every day last week, NHS hospitals in England were at bursting point".