BITCOIN NEWS: Pay Attention to January 26th. (SERIOUSLY)
A crash when referencing free markets is generally defined as a 10% decline over a short period of time. This movement generally induces panic selling that can either exacerbate the selling over time (snowball) or simply give deep pockets the chance to get some cheap entries only to see markets reestablish new highs fairly soon.
The difference in cryptocurrency is that 10% ‘crashes’ have become passé and so rarely cause panic. This seems to demand a premium to the 10% level as inducing panic requires a greater decline. The Bitcoin market has seen a crash or two; it just had one and it was very nearly 50%.
A good estimate would take some work. Search historical price charts for very high volume down days and then average The levels at which those panic selling days are typically caused. That would be a good generalization and a decent answer.
Note: Remember this January thing is normal and a yearly occurence. Even among all the FUD going around BTC is following a normal correction. BTC WILL go much higher than previous ATH starting in FEB. Just be patient and do something else in the meantime.
I am holding my deep pockets till the 26th!
Bitcoin will bounce back buddy, scalability updates are on the way with Lightning Network and Segwit which will reduce fees and increase speed. More big money is on its ways as well, Goldman Sachs will launch crypto trading desk in June 2018. Also, note that price corrections and pullbacks happen all the time in the crypto market. HOLD people!