In this study we estimate the prospective tidal current energy resources off the south and west coasts of Korea and explore the influence of modeling tidal current energies based on 15-day versus month-long data records for regimes with pronounced perigean/apogean influences. The tidal current energy resources off southern and western Korea were calculated using 29-day in situ observation data from 264 stations. The resultant annual energy densities found at each station were categorized into six groups, with a greater percentage of sites falling into the lower-energy groups: 1.1% for >10 MWh·m−2; 2.7% for 5 to 10 MWh·m−2; 6.8% for 3 to 5 MWh·m−2; 9.1% for 2 to 3 MWh·m−2 and 80.3% for <2 MWh·m−2. Analysis shows that the greatest concentration of high annual energy densities occurs in the Jeonnam Province coastal region on the western tip of southwest Korea: 23 MWh·m−2 at Uldolmok, 15 MWh·m−2 at Maenggol Sudo, 9.2 MWh·m−2 at Geocha Sudo and 8.8 MWh·m−2 at Jaingjuk Sudo. The second highest annual energy density concentration, with 16 MWh·m−2, was found in Gyudong Suro, in Gyeonggi Province’s Gyeonggi Bay. We then used data from the 264 stations to examine the effect of perigean and apogean influences on tidal current energy density evaluations. Compared to derivations using month-long records, mean annual energy densities derived using 15-day perigean spring-neap current records alone overestimate the annual mean energy by around 10% whereas those derived using only the apogean records underestimate energy by around 12%. In particular, accuracy of the S2 contribution to the energy density calculations is significantly affected by use of the 15-day data sets, compared to the M2 component, which is relatively consistent. Further, annual energy density estimates derived from 29-day records but excluding the N2 constituent underestimate the potential resource by about 5.4%. Results indicate that one month of data is required to accurately estimate tidal current energy in regimes showing pronounced perigean and apogean differences in spring-neap tidal current patterns and that inclusion of the N2 constituent in calculations is preferable. This finding has widespread applicability for green energy resource assessments, for example, in regions of the Unites States Atlantic coast and in New Zealand.