Say for example, I bought $1000 worth of Bitcoin at $15,000.00.
It goes up to say $16,000.00.
What's the best formula to calculate my notional account balance (excluding transaction fees, to keep it simple)?
Thanks
new balance = old balance x new price / old price
In your example,
new balance = $1000 x $16000 / $15000 = $1066.67
But it might be easier to just keep track of the amount of btc and its value.
btc = sale amount / btc price
Then anytime you want to know how much you have
new balance = btc x new price
In your example, you bought $1000 worth of BTC at $15000, so you have
btc = $1000 / $15000 = 0.06666666 BTC
and the price is now $16000, so your BTC is now worth
new balance = 0.06666666 x $16000 = $1066.67