Tiers:

There are 5 tiers of bonus potentials for accessories and armors.
For weapons, secondary weapons and emblems, the tiers for STR, DEX, INT, LUK, ATT and Magic ATT follows that of regular potentials.

Based on STR, DEX, INT and LUK:

Level Rare Epic Unique Legendary
0 - 20 1% 1% 2% 3%
21 - 50 1% 2% 3% 4%
51 - 90 1% 3% 4% 5%
91 - 200
(91 - 150 GMS/TMS)
2% 4% 5% 7%
201+
(151+ GMS/TMS)
3% 5% 6% 8%

All stat % are 1 rank below the stated rank

Based on HP:

Level Rare Epic Unique Legendary
0 - 20 1% 1% 2% 3%
21 - 50 1% 2% 3% 5%
51 - 90 1% 3% 5% 7%
91 - 200
(91 - 150 GMS/TMS)
2% 5% 7% 10%
201+
(151+ GMS/TMS)
3% 6% 8% 11%