We demonstrate that long-term tidally-induced changes in extreme sea levels affect estimates of major flood hazard in a predictable way. Long-term variations in tides due to the nodal and perigean tidal cycles influence extreme sea levels at 234 global tide gauges out of a total of 344. Results show regions where the amplitudes of the modulations are particularly relevant in the 100-year return sea level; the eastern coast of China, the northwestern and northeastern coasts of Australia, the northeast coast of Pacific, and the eastern coast of Europe, reaching up to ~22 cm in western France. We identify locations that are currently in a positive phase of the modulation and therefore at a higher risk of flooding, as well as when (year) the next peak of the nodal/perigean modulations is expected to occur. The timing of the peak of the modulation is spatially coherent and influenced by the relative importance of each cycle (nodal or perigee) over the total amplitude. An evaluation of four locations suggests that the potentially flooded area in a 100-year event can vary up to ~45% (in Boston) as a result of the long-term tidal cycles; however, areal change is often smaller due to local topography and tidal characteristics (6-13%). We conclude that tidally-modulated changes in extreme sea levels can alter the potentially inundated area in a 100-year event and that the traditional, fixed 100-year floodplain is inadequate for describing coastal flood risk.