Note: Enabling "Virtual Levels" in the Settings will show the player if they would be on a level higher than 99 ( 120), even though this gives almost no benefits. Pet drop rate calculations are based on your Virtual Level, however note that calculation will use your Virtual Level regardless of the setting.
The experience difference between level [math]\displaystyle{ L1 }[/math] and level [math]\displaystyle{ L }[/math] is approximately [math]\displaystyle{ \left\lfloor \frac{1}{4} \left( L1+300\times 2^{\frac{L1}{7}} \right) \right\rfloor }[/math]. The table below shows this experience difference for each level and also the cumulative experience from level 1 to level [math]\displaystyle{ L }[/math]. Note that experience levels are nonlinear and so the amount of experience between 1 and 92 is the same as the amount of experience between 92 and 99. Experience also doubles about every 7 levels. For example, the experience between 7 and 8 is 138 and the experience between 14 and 15 is 274, which is roughly double.
The base game has a maximum skill and Mastery level of 99, with the Throne of the Herald Expansion the skill level maximum is increased to 120.
1 
0 
0

26 
8,740 
898

51 
111,945 
10,612

76 
1,336,443 
126,022

101 
15,889,109 
1,497,949

2 
83 
83

27 
9,730 
990

52 
123,660 
11,715

77 
1,475,581 
139,138

102 
17,542,976 
1,653,867

3 
174 
91

28 
10,824 
1,094

53 
136,594 
12,934

78 
1,629,200 
153,619

103 
19,368,992 
1,826,016

4 
276 
102

29 
12,031 
1,207

54 
150,872 
14,278

79 
1,798,808 
169,608

104 
21,385,073 
2,016,081

5 
388 
112

30 
13,363 
1,332

55 
166,636 
15,764

80 
1,986,068 
187,260

105 
23,611,006 
2,225,933

6 
512 
124

31 
14,833 
1,470

56 
184,040 
17,404

81 
2,192,818 
206,750

106 
26,068,632 
2,457,626

7 
650 
138

32 
16,456 
1,623

57 
203,254 
19,214

82 
2,421,087 
228,269

107 
28,782,069 
2,713,437

8 
801 
151

33 
18,247 
1,791

58 
224,466 
21,212

83 
2,673,114 
252,027

108 
31,777,943 
2,995,874

9 
969 
168

34 
20,224 
1,977

59 
247,886 
23,420

84 
2,951,373 
278,259

109 
35,085,654 
3,307,711

10 
1,154 
185

35 
22,406 
2,182

60 
273,742 
25,856

85 
3,258,594 
307,221

110 
38,737,661 
3,652,007

11 
1,358 
204

36 
24,815 
2,409

61 
302,288 
28,546

86 
3,597,792 
339,198

111 
42,769,801 
4,032,140

12 
1,584 
226

37 
27,473 
2,658

62 
333,804 
31,516

87 
3,972,294 
374,502

112 
47,221,641 
4,451,840

13 
1,833 
249

38 
30,408 
2,935

63 
368,599 
34,795

88 
4,385,776 
413,482

113 
52,136,869 
4,915,228

14 
2,107 
274

39 
33,648 
3,240

64 
407,015 
38,416

89 
4,842,295 
456,519

114 
57,563,718 
5,426,849

15 
2,411 
304

40 
37,224 
3,576

65 
449,428 
42,413

90 
5,346,332 
504,037

115 
63,555,443 
5,991,725

16 
2,746 
335

41 
41,171 
3,947

66 
496,254 
46,826

91 
5,902,831 
556,499

116 
70,170,840 
6,615,397

17 
3,115 
369

42 
45,529 
4,358

67 
547,953 
51,699

92 
6,517,253 
614,422

117 
77,474,828 
7,303,988

18 
3,523 
408

43 
50,339 
4,810

68 
605,032 
57,079

93 
7,195,629 
678,376

118 
85,539,082 
8,064,254

19 
3,973 
450

44 
55,649 
5,310

69 
668,051 
63,019

94 
7,944,614 
748,985

119 
94,442,737 
8,903,655

20 
4,470 
497

45 
61,512 
5,863

70 
737,627 
69,576

95 
8,771,558 
826,944

120 
104,273,167 
9,830,430

21 
5,018 
548

46 
67,983 
6,471

71 
814,445 
76,818

96 
9,684,577 
913,019

22 
5,624 
606

47 
75,127 
7,144

72 
899,257 
84,812

97 
10,692,629 
1,008,052

23 
6,291 
667

48 
83,014 
7,887

73 
992,895 
93,638

98 
11,805,606 
1,112,977

24 
7,028 
737

49 
91,721 
8,707

74 
1,096,278 
103,383

99 
13,034,431 
1,228,825

25 
7,842 
814

50 
101,333 
9,612

75 
1,210,421 
114,143

100 
14,391,160 
1,356,729

The formula to calculate the amount of experience needed to reach level [math]\displaystyle{ L }[/math] is:
 [math]\displaystyle{ \text{Experience} = \left \lfloor{\frac{1}{4}\sum_{\ell=1}^{L1}}\left\lfloor{\ell + 300\cdot2^{\ell/7}}\right\rfloor\right\rfloor }[/math]
If the floor functions are ignored, the resulting summation can be found in closed form to be:
 [math]\displaystyle{ \text{Experience} \approx \frac{1}{8} \left( {L}^{2}  L + 600 \, \frac{{2}^{L/7}2^{1/7}} {{2}^{1/7}1} \right) }[/math]
The approximation is very accurate, always within 100 experience but usually less than around 10 experience.