Nothing guaranteed, of course this is only a rough estimate! You can also calculate rented mining by setting “Power consumption” to 0 and “Cost of mining hardware” to the rent per time frame. Default values are for a system of four 6870s.
Extrapolating bitcoin difficulty or price is pure voodoo. It is much easier to predict the relationship of the two parameters in form of the Mining Factor. The Mining Factor 100 is the value in USD of the bitcoins you can generate if you let a 100MHash/s miner run for 24 hours. If the Mining Factor 100 rises above $2 or so everybody buys mining equipment and thus increases difficulty. If it falls people will stop mining eventually. The estimate starts with the current Mining Factor and decreases it exponentially such that the decrease accounts for the factor decline per year. Please note that a profit/loss by holding the coins is not accounted for in this estimate.
Things to consider that might eat into your profit:
- The values above are only a snapshot. The network and markets are moving quickly. Check out these diagrams to get a feeling for it.Looks like if your mining operation is not profitable now, it probably will not be in the future.
- With rising bitcoin exchange rates it might be more profitable to buy bitcoins than to mine. There are spreadsheets available in this thread or this one (with some FPGA data) for a more custom calculation.Bitcoin exchanges: MtGox, Tradehill, CryptoXchange.
- The calculation is based on average block generation time. The closer the average generation time is to the time frame the more the resulting revenue depends on luck.
- You will have to pay mining pool fees from close to nothing up to 3% depending on the pool. Unless you want to do pool hopping you should go to a pool with hopping protection. I recommend Arsbitcoin and EclipseMC (with namecoin merged mining). P2Pool is a new completely decentralized alternative.
- You will get somewhere from 1% to 3% of “stale shares”. Thread.
- When the block count will hit ~200000 some time around December 2012 the generation reward will go down to 25BTC. This might partly be compensated by falling difficulty, raising prices, higher transfer fees, etc.
- A mining computer generates a lot of heat as a byproduct. This can impact your heating/airconditioning costs depending on outside temperatures. Other byproducts could be noise and an angry wife.
- Do you have lots of experience with and like working with computers during lonesome nights? You have to spend quite some time to set up the system (easily several days!) and watch it.
- You will not get a 100% uptime.
- You will probably not be able to reach the highest values in the Mining Hardware Comparison. Some bragging / measuring error and extensive overclocking of the cards is involved here.
- Scaling effects: three cards in one rig do worse than a single card because it gets harder to get out the heat. Results in the list above do not reflect the number of cards.
- A disruptive technology like ASIC chips could show up and make GPU mining less profitable.
- Politics and legal issues might affect the bitcoin market.
Possible additional benefits:
- With namecoin merged mining you might be able to squeeze out a little more or be able to register a couple of .bit domains.
- You might be able to save heating costs when it’s cold outside. Some people use watercooled rigs for floor heating.
- You can use your rig as an internet radio or media PC or a server in general.
For suggestions, infos or links on the topic to add, please contact me directly (info [at] bitcoinx.com) or in this thread on the bitcoin forum.