From Diablo Wiki
The Paragon system was added to Diablo 3 shortly after release, in the v1.0.4 patch on August 22, 2012. The system was an end game feature that provided additional levels and bonuses for a character once they reached the max level of 60. At that point, the max-level character could start earning Paragon Levels, each of which added passive bonuses 3% to Magic Find and Gold Find, plus the same attribute bonuses as a normal level up (3 to the class main stat, 2 vitality, 1 to the other two stats). The maximum was Paragon 100, and many players set "P100" as their end goal.
The Paragon system was completely overhauled for Diablo 3 version 2, in what the developers called Paragon 2.0. That system is what players see today in Diablo 3 and Reaper of Souls. Paragon 2.0 changed Paragon experience to work account-wide, so every character on the account, of any level, received the same full number of Paragon points. Each Paragon Level grants a point that can be spent in any of the four bonus fields in four different Paragon Tabs, allowing for greater character customization. Paragon 2.0 also makes leveling up a new character much quicker and easier, as Paragon Points are available to all characters on the account, even brand new level 1 heroes.
 Paragon Points
In the Paragon 2.0 system, each level grants a new Paragon Point, alternating between the four tabs. The first Paragon Point must be spent in the Core Tab, the second in the Offense Tab, and so on, until all tabs have 200 points and all the fields are maxed out at 50 points at Paragon 800. Points above that are awarded only to the Core Tab, where the Mainstat, and Vitality bonuses are the only two that do not max out at 50 points and can be boosted forever.
 Core Tab
The Core Tab has the only two bonuses that do not max out at 50 points. Movement Speed is also an odd one, since the property has a hard cap at 25% from Items + Paragon Points. Thus a character with 20% Movement Speed from gear would only gain another 5% from Paragon Points, and any boost over that would be wasted. (This is why it's best to enchant movement speed off of items, for a more useful bonus that won't be rendered redundant by Paragon Points.)
- Mainstat: +5 per point, no hard cap.
- Vitality: +5 per point, no hard cap.
- Movement Speed, +0.5% per point, maxing out at +25% with 50 points.
- +Maximum Resource:
- Barbarian: +1 to maximum Fury per point.
- Crusader: +1 to maximum Wrath per point.
- Demon Hunter: +0.5 to maximum Hatred per point. (Discipline is not boosted by Paragon points.)
- Monk: +1 to maximum Spirit per point.
- Witch Doctor: +4 to maximum Mana per point.
- Wizard: +1 to maximum Arcane Power per point.
 Offense Tab
Critical hit Chance was reduced from .2% to .1% per point during PTR testing, lowering the maximum from 10% to 5%. Prior to that, ChC was clearly the best stat to boost.
- Attack Speed: +.2% per point, for a maximum of +10% at 50 points.
- Cooldown Reduction: +2% per point, for a maximum of +10% reduction at 50 points.
- Critical Hit Chance, +.10% per point, for a maximum of 5% at 50 points.
- Critical Hit Damage, +1% per point, for a maximum of 50% at 50 points.
 Defense Tab
The Defense tab shifted a bit during development. The initial version on the PTR had Life, Armor, Dodge, and Resist All. Dodge was subsequently removed entirely from Paragon Point bonuses.
- Life. Increases +.50% Life per point, to a maximum value of +25% Life.
- Armor. Increases +.50% Armor per point, to a maximum value of +25% Armor.
- All Resistance: +5 per point, with a maximum of 250.
- Life Regeneration, +165.1 per point, for a maximum of +8252 life per second.
- Originally +33 per point with a maximum of +1650, before Patch 2.1 boosted it as part of the general healing and combat engine changes.
 Utility Tab
The Utility Tab changed several times during testing. In the initial iteration during PTR testing it held Magic Find, Gold Find, +maximum resource, and Movement Speed. Paragon point options were shuffled between the tabs and some were removed or replaced during development.
The current stats in the live game are:
- Area Damage: +1% per point, max of +50%.
- Resource Cost Reduction: 0.2% per point, maximum of 10% cost reduction.
- Life on Hit: 82.5 per point, maxing out at 4125.
- Gold Find: +1% per point for a maximum of +50%.
- Gold Find boosted by gear or Paragon Points switched from additive to multiplicative in Patch 1.0.6, granting much higher Gold Find on higher difficulty levels and making points here worth the expense for many gold-poor players.
 Archived Paragon Information
The following archived content describes how the Paragon system worked in D3v. It is obsolete information (though the Diablo 3 console still works similarly) and is preserved here purely for historical interest.
 Original Paragon Level Details
- After a player reaches level 60, killing monsters and completing combat challenge streaks (Killing Blow, Massacre, etc) will begin to award experience towards Paragon levels
- There are 100 Paragon levels
- Every Paragon level will reward you with:
- Core stats such as Strength, Dexterity, Intelligence, and Vitality in amounts similar to what you’d gain from a normal level
- 3% Magic Find and 3% Gold Find
- In addition, a distinctive border will surround your character portrait in the in-game party frame to denote your Paragon progression, with a new frame earned after every ten levels. Your Paragon level will also be visible to other players wherever your normal level is shown.
- Nephalem Valor now grants +15% Bonus Experience per stack, as well as +15% to Magic Find and Gold Find
- Magic Find will now cap at 300% (Nephalem Valor bonuses, Fortune shrines, and multiplayer bonuses will stack beyond this cap).
- Magic Find is no longer averaged among all players in a multiplayer game.
 Paragon Levels Experience
Players quickly datamined the patch for precise details about the experience gains required for Paragon Levels. Most players can advance through the first 10 or 15 Paragon levels fairly quickly, but the progress slows down in the 20s and 30s, and then grows markedly slow past level 40. Above level 80 further advances become more of a grind.
Though the total experience needed is considerable, it was just two weeks before the first character reached Paragon level 100. The winner was a Barbarian named Alkaizer, who dinged to the top on September 6, 2012 and became famous by giving his name to the popular Act Three experience farming Alkaizer run.l
Initially, characters into the Paragon levels did not gain experience from quest rewards or other bonuses besides monster killing. (Experience shrines didn't even spawn in Inferno at that point.) Subsequent patches enabled these missing features, and added any more ways to gain rapid experience with more gear bonuses, bigger bonuses from multiplayer games, and more.
 Experience Charts
Huge table showing current and cumulative experience required for all 100 Paragon levels. Level 50 requires 2.1 billion experience and is just over 20% of the way to Paragon 100. The actual halfway point comes around level 78.5, when a character has earned 5.2 billion of the 10.4 billion experience required for P100.
- For Levels 1-60, experience requirements increase at a rate of 1,440,000/level.
- For Levels 61-70, experience requirements increase at a rate of 2,880,000/level (=2*1,440,000).
- For Levels 71-80, experience requirements increase at a rate of 5,020,000/level (=3.5*1,440,000).
- For Levels 81-90, experience requirements increase at a rate of 6,480,000/level (=4.5*1,440,000).
- For Levels 91-100, experience requirements increase at a rate of 8,640,000/level (=6*1,440,000).
| Experience points
(needed for level)
| Experience points total
(from level 0)
| Other stats
| Magic and Gold|
* * Table courtesy of Diablo.kalais.net.
A handy pie chart giving a proportional view of the total Paragon Level experience gain. The amount per level increases steadily from 1-59, and then increases more steeply at levels 60, 70, 80, and 90.
Several screenshots showing off aspects of the original Paragon system.