If you would like to see when your cash flow is due to drop below a certain amount, you can set a threshold.  

By default Float will tell you the date that your cash balance is due to drop below 0, but you can change this to an different amount by clicking the blue 0 on the side panel, as shown below:
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From here you can set an amount. If you have an overdraft or line of credit, a negative amount can be set by using a minus sign.