Bitcoin graphics card calculator

I was confused by the profitability calculators I saw because I find it hard to get a feeling for how the difficulty influences my yield and also for where I can expect the difficulty to go, since it's such an abstract value.

So I now use what to me is more intuitive: there's a (more or less) fixed number of 3, 600 BTC gained from mining each day, until the block reward halves in 2017. Those coins can be viewed as being shared by the whole network proportionally to the computing power of each player.

So, let's assume a network power of 360 Thash/s, which seems not far away as I write this, and makes for easy calculation, then for every Ghash/s that your equipment brings to the table, you get 0.01 BTC per day.

If you're solo mining, this is overly simplified, but the general direction of solo mining is that your actual yield will only on average match the theoretical one, so if you're much much smaller than the network (likely), then your variance gets so high that it becomes a lot like a lottery.