The Difficulty Class for the roll. This is the number you have to beat to succeed, adding together your roll and modifier.

DC	Simple DCs by Proficiency Rank
10	Untrained
15	Trained
20	Expert
30	Master
40	Legendary
DC	Level Based DCs
14	Level 0
15	Level 1
16	Level 2
18	Level 3
19	Level 4
20	Level 5
22	Level 6
23	Level 7
24	Level 8
26	Level 9
27	Level 10
28	Level 11
30	Level 12
31	Level 13
32	Level 14
34	Level 15
35	Level 16
36	Level 17
38	Level 18
39	Level 19
40	Level 20
42	Level 21
44	Level 22
46	Level 23
48	Level 24
50	Level 25

The modifier to the roll. Add to the die roll to get the total; try to beat the DC.

Proficiency Bonus	Proficiency Rank
0	Untrained
PC level + 2	Trained
PC level + 4	Expert
PC level + 6	Master
PC level + 8	Legendary