identifying a fracture fluid leak-off curve that comprises a plurality of time-dependent pressure signal values of a fluid in a first wellbore formed in a subsurface formation, each of the plurality of time-dependent pressure signal values comprising a pressure change in the fluid in the first wellbore that is induced by formation of a hydraulic fracture from a second wellbore in the subsurface formation by a hydraulic fracturing fluid that comprises proppant;

determining a time value corresponding to one of the plurality of time-dependent pressure signal values, the time value associated with proppant landing time in the hydraulic fracture;

determining a plurality of extrapolated time-dependent pressure signal values based on, and prior to, the determined time value;

generating at least one curve that comprises the plurality of extrapolated time-dependent pressure signal values;

determining an intersection of the fracture fluid leak-off curve and the generated at least one curve;

determining a particular time-dependent pressure signal value at the intersection;

based on the determined particular time-dependent pressure signal value, determining a proppant-area dimension of the hydraulic fracture formed from the second wellbore; and

determining the proppant-area of the hydraulic fracture based on the determined proppant-area dimension of the hydraulic fracture; and

generating one or more graphical representations of the determined proppant-area of the second hydraulic fracture for output to a graphical user interface (GUI).