The additional 378 trips will shorten waiting times by up to two minutes, it said yesterday.
Commuters can expect more trains to pull up at stations on weekday evenings, Saturday mornings and evenings and Sunday afternoons and evenings.
The extra trips, the fifth lot offered this year, will run from Saturday till Dec 30.
SMRT's vice-president of rail operations Vincent Tan said more commuters take the train in the last two months of the year when doing their Christmas shopping.
'This year, we are continuing the tradition of providing additional train trips for their convenience,' he said.
About a third of the extra trips each week will be on Saturday. On weekends, commuters on the North-South and East-West lines in both directions will have shorter waits.
For example, an extra 35 train trips will be added each way to North-South Line trains plying between Marina Bay and Yishun from 5pm to 11.45pm on Saturdays.
From next Monday, SMRT will roll out an additional 15 trips in each direction for the North-South Line, and another 10 in each direction for the East-West Line on weekday evenings.
The train operator has added about 900 trips a week so far this year, with the majority rolled out in May.