Rewards are charged the following fees: 15% of reward and a fixed cost of $10 per node per month, scaled to the staking shares that you own.
To illustrate how the fees are calculated, we shall use an arbitrary coin, “ARB”. ARB gives out a reward of 50 ARB every time, and is rewarded every 2 days (i.e. 15x in a month), and ARB is trading at $0.80.
For each reward, the fee is thus:
Fixed cost: ($10 / 15) / $0.8 = 0.83333 ARB
Reward fee: (50 ARB - (fixed cost)) * 15%
= (50 ARB - 0.83333 ARB) * 0.15
= 7.3750005 ARB
Total fee for each reward: (Fixed cost) + (Reward fee)
= 0.83333 ARB + 7.3750 ARB
= 8.20833 ARB for each reward
If you own 2.5% of all the ARB nodes, the effective fee to you would be 0.020520825 ARB.
The remaining rewards, i.e. 41.66667 ARB will be distributed to all stakers.