The notification on election will be issued next Monday and the candidates will get a week's time to fill nominations. The last date for filing nominations will be April 25, a senior official said.
The scrutiny of the nominations will be conducted on April 27 and withdrawal of candidature can be done till April 30.
"The votes will be polled on May 15 and the counting will take place on May 17," the official said.
Delhi Congress has been demanding that by-elections be held and had also filed a petition in Delhi High Court for the same. The court had directed for holding of the by-elections.
The posts of councillors in the 13 wards were vacant after nine of them resigned on becoming legislators in the 2013 Assembly election and four after the 2015 elections.