According to Jain belief, there is no next Tirthankara in this current Avasarpiṇī time cycle, because Bhagwan Mahavira is the 24th and final Tirthankara of this half-cycle.

In the next Utsarpiṇī cycle, the first Tirthankara is said to be Padmanabha.

So, in short:

• Current cycle: no next Tirthankara after Mahavira
• Next cycle: Padmanabha will be the first Tirthankara