TL;DR: The way the bankroll commission rate is calculated is changing. This only affects bankroll investors, so players can skip to the next post.
The intention behind the dynamic commission rate introduced just a few months ago was to reduce the size of the bankroll to a more reasonable one and to find an appropriate commission rate. Today, however, the bankroll is larger than ever. The change clearly isn't fulfilling its purpose, so I am adjusting the formula. At the bankroll's current size of nearly $150m this represents a significant increase in the commission rate, which I hope will move investors to realize some of their profits and divest from the bankroll.
Starting on March 2 the commission rate will be calculated like this:
bankroll * (360-day moving average of BTCXDR) / 55,000,000 XDR
Please see
https://www.bustabit.com/help/investing for details on when and how the exchange rates are updated and how the commission rate is calculated.
Even though bustabit exclusively uses Bitcoin, the wager volume it sees is stabler in terms of purchasing power.
Special drawing rights (XDR) are a currency basket defined by the IMF that consists of USD, EUR, CNY, JPY and GBP. Pegging the commission rate to special drawing rights encourages a reasonable bankroll size regardless of Bitcoin's price without being reliant on any single country's currency.
Despite the huge bets bustabit sometimes sees, more than 99% of its wager volume (!) could be served with a bankroll of "only" $40m. For bustadice, where unlike on bustabit the result of players' bets are not correlated, the number is smaller still. To give a concrete number, I would be happy to see the bankroll decrease by two thirds to about $50m in value. This is what the factor of 55,000,000 XDR targets.
Finally, using the moving average of the exchange rate compensates for the short-term volatility of Bitcoin's price and makes commission rates more predictable.
I owe an apology to bankroll investors for adjusting the formula again so soon. Several people including Ryan suggested incorporating the price of Bitcoin in the calculation back in November, but I wanted to keep things simple and decided on a Bitcoin target instead. Unfortunately the price of Bitcoin had more than doubled less than a month later. With the commission rate now accounting for Bitcoin's price further changes should at most be necessary every few years.