The time period over which the value is calculated
Current economic conditions and market trends
Long-term vs. short-term valuation considerations
Example
Let's say you have 0.5 BTC in one exchange and 0.3 BTC in another. You check the current market price at $40,000 per BTC. Adding any recent transaction fees of $50 might give you a total value of $36,050.
Question
How often should I recalculate my Bitcoin holdings?
To stay up-to-date with your investment's worth, it's a good idea to recalculate your holdings at least monthly or after significant market changes.
Risk management you can actually use
Risk per trade = account equity × risk% (e.g., 1%).