Let's say I have a currency trading app. I start with $100 USD, and after 4 weeks, though trades, I now have $200 USD. My P&L would be 100$ or up $100.
So the calc would be: P&L = start_value - current_value
Now, in a similar scenario, I start the month with $100 USD, 2 weeks later I add $50 USD, 2 weeks later I now have $200 USD. How do I calculate the P&L for the last four weeks, considering I added $50 in the middle?