Was something changed recently? I've been getting less and less ether per block - is this tied to difficulty level?
I thought difficulty would affect the rate of mining a block, not the number of ether per block. My last block got me 3.75 Ether.
If you got 3.75 ether, this was an uncle mining reward. Kind of the "second place" of mining on Ethereum. You found a solution but someone else found the solution before you. Thankfully for you, it was soon enough from the original block that a reward was paid out.
It's still 5 ether per block for a mining reward.
Update: As of Oct-16-2017 05:22:11 AM +UTC (Block #4370000), it's 3 ether per block
Update: As of Feb-28-2019 07:52:04 PM +UTC (Block #7280000), it's 2 ether per block.
The reduction in ether reward is due to the price increase in Ether. The reductions in block rewards are in an effort to reduce inflation by reducing the newly-available supply of ETH https://media.consensys.net/the-thirdening-what-you-need-to-know-df96599ad857
The mined block is an uncle. The uncle reward formula is
(U_n + 8 - B_n) * R / 8 where
R is the static reward of
U_n is the uncle number and
B_n is the block numer, so:
Here's an example:
B_n = 1337, R = 5 U_0 = (1336 + 8 - 1337) * 5 / 8 == 4.375 U_1 = (1335 + 8 - 1337) * 5 / 8 == 3.750