Effective August 7, 2014 Negative Boost Effects On The Opposite Element Were Removed 
Calculating Earnings Summary
The boosted earning rate can be calculated using the below equation: Boosted Income = (Base Income x (1 + 0.3 * Number of boosts)) When multiplying if there is a decimal in your product round it up the next whole number.

Calculating Earnings With Positive Element Boosts
Boosts each provide an increase of 30% to the earning rates of dragons of the same element that are housed on the island that the boost is placed on. Depending on the boost and dragon placement, a dragon's earnings rates can be affected in a positive way.
Boosts do not affect epic dragons without primary elements (besides monolith dragons or any of the gemstone dragons at this time. To calculate the earning rate of a dragon, the player will need to determine how many boosts are affecting that dragon. Then, the player will need to add that amount from his/her dragons' earnings. The effects of one positive boost on a dragon with a base earning rate of 100 would be calculated as: 100 + (100*30%) = 130
100 + 2*(100*30%) = 160
100 + 3*(100*30%) = 190
100 + 4*(100*30%) = 220
The player simply needs to place the appropriate number of positive boosts into the formula for their given situation. Boosted Income = (Base Income x (1 + 0.3 * Number of boosts))
When multiplying if there is a decimal in your product round it up the next whole number.

Rounding Ranges
Once a dragon's displayed earn rate goes over 900 DragonCash per minute, a dragon's earn rate will get rounded up to cerain values depending on how much they earn.
Range of Displayed Rates  Rounded To 

900999  1,000 
10001,199  1,200 
1,2001,499  1,500 
1,5001,999  2,000 
2,0002,999  3,000 
Example: A Tien Dragon's base earning rate at level 20 is 992, if affected by four positive boosts, the calculation would be:
992 * 4*(100*30%) = 2,182, which gets rounded up to 3,000.
Outdated Calculating Method With Positive and Negative Boosts
Boosts each provide an increase of 20% to the earning rates of dragons of the same element, and a decrease of 20% to the earning rates of dragons of the opposite element, that are housed on the island that the Element Boost is placed on. Depending on Boost and dragon placement, a dragon's earnings can be affected in both positive and negative ways.
Boosts do not affect the Epic Dragons or any of the Gemstone Dragons at this time. To calculate the earning rate of a dragon, the player will need to determine how many Element Boosts are affecting that dragon, and whether the boosts are positively or negatively affecting the dragon. Then, the player will need to add or subtract that amount from your dragons' earnings. The effects of one positive OR one negative boost would be calculated as: 100 + (100*20%) = 120 100  (100*20%) = 80 It is important to note that the effects of Boosts are cumulative, meaning that the percentages are calculated in succession. If a dragon's base earning rate is 100, and was then affected by two positive boosts, the calculation would be: 100 + (100*20%) = 120 > 120 + (120*20%) = 144 Another important fact is that it doesn't matter if the positive Boosts are calculated first and then the negative Boosts are calculated from that total or vice versa. What matters is that one positive Boost does NOT simply cancel out one negative Boost. We will use the previous example again to illustrate calculating two positive Boosts and one negative Boost: 100 + (100*20%) = 120 > 120 + (120*20%) = 144 > 144  (144*20%) = 115.2 (round to 115)
100 + (100*20%) = 120 > 120 + (120*20%) = 144 >. 144  (144*20%) = 115.2 > 115.2  (115.2*20%) = 92.16 (round to 92)
Dragon's base earning rate + positive Boost #1 + (positive Boost #1*positive Boost #2)  negative Boost #1*(positive Boost #1*positive Boost #2)  negative Boost #2*(negative Boost #1*positive Boost #1*positive Boost #2) = actual earning rate The player simply needs to place the appropriate number of positive and negative boosts into the formula for their given situation. (gpm x 1.2^{y}) x 0.8^{z} gpm = dragoncash per minute with no boosts y = number of positive boosts z = number of negative boosts

Dragon Earning Rates Tables
The following page has tables of the earning rate per minute each dragon earns without boosts. Use this page to apply your Boost Calculations to:
Notes
Dragons  Breeding  Eggs  Buildings  Islands  Habitats  Decorations  Friends 