Find where it starts
Dry the floor and the outside of the toilet completely, then watch. Water that appears at the base after flushing points to the seal. Water that runs down from the tank, the supply line or the tank bolts points higher up. Beads of water all over the tank on a humid day are condensation.
Likely causes
- A compressed or broken wax ring between the toilet and the floor flange
- Loose floor bolts that let the toilet rock and break the seal
- A cracked toilet base
- A leaking supply line, shutoff valve or tank-to-bowl gasket
Why not to wait
A failed seal lets waste water seep under the flooring every time the toilet is flushed. It can rot the subfloor, stain the ceiling below and let sewer gas into the room.
When professional help makes sense
Replacing a wax ring means pulling the toilet and checking the flange underneath, which is where most repeat leaks start. If the floor feels soft around the toilet, have it looked at soon.