Pulse transit time (PTT) often shows strong correlation with blood pressure (BP) and may therefore represent a means for achieving continuous, non-invasive, and cuff-less BP monitoring. However, construction of the subject-specific curve needed to calibrate PTT to BP conventionally requires simultaneous measurements of PTT and BP during an experimental perturbation that varies BP over a significant range. We propose a technique for perturbationless calibration of PTT to BP. This technique constructs the calibration curve from central and peripheral BP waveforms by exploiting the natural pulsatile variation in the waveforms via a nonlinear tube-load model. We conducted initial testing of the technique in animals by applying it to the waveforms during a baseline period and then predicting mean BP during subsequent major hemodynamic interventions via PTT calibrated with the resulting curve. The bias in the mean BP error was 4.9 mmHg, while the precision in this error was 7.6 mmHg.