The Forsa institute said both parties were tied at 222.
The Infratest dimap institute released the same estimate of a draw between the two biggest parties following the inconclusive election, if the SPD manages to win extra seats granted based on Germany's complex proportional voting system.
Although the Social Democrats scored fewer votes than Angela Merkel's Christian Democrats, it can win extra seats.
Tipping the scales were so-called "overhang" seats, which derive from the two votes that each German casts when he goes to the polls.
In the first vote, the candidate with the most votes in each constituency is elected to one of 299 seats, half of the 598-seat Bundestag chamber.
The second vote decides the allocation of the other 299 seats via the state lists using a proportional system of calculation.
Exit polls initially showed Angela
Merkel with a narrow lead
Those seats are distributed based on the number of votes obtained by party lists, with people at the top of their lists having the best chance of getting in.
Overall, it means a party can win seats individually and as a group, and if there is a difference in the number obtained under either system, the party is allowed to keep the extras, which are known as the "overhang" seats.
As a result, the Bundestag elected at the last general election in 2002 had a total of 603 instead of 598 seats.
Once the Bundestag has been chosen, the federal chancellor is elected with an absolute majority of parliamentary votes.