Elderly people often use a smaller percentage of their base of support during maximal weight shifting, which leads to balance instability, that can lead to frequent falls and serious injuries. Even the most active people cannot reach theoretical limits of stability, therefore the need to investigate the functional BOS i.e. the real stability boundary and the factors that can affect this ability. The new index of anterior stability limit (IASL) explaining the functional base of support (BOS) in sagittal plane (while participants voluntarily displace their COP in the front direction) that can assess fear and risk of falling. Twenty five students of the University of the Third Age voluntarily participated in the study. The force plate measurements allowed to investigate functional limit of stability in addition to clinical tests (BBS, Duncan, TUG). The FES-I questionnaire was used to evaluate fear of falling. Additionally, the anthropometric parameters of the foot were measured. The IALS is proportion between range of COP displacement during maximum forward lean and distance from the ankle joint to the head of first metatarsal bone. The Pearson's linear correlation between FES-I, BBS, Duncan test, TUG test and IASL was conducted. High negative correlation was observed between IASL and main scores of FES-I ( r = −0.64, P < 0.05) and also between IASL and TUG test ( r = −0.76, P < 0.05). Positive correlation was noticed between IASL and Duncan test ( r = 0.66, P < 0.05), as well as BBS ( r = 0.6, P < 0.05). The use of IASL indicate that elderly people used on average 70% of their functional BOS. Use of smaller functional BOS determines increase the fear of falling. Lower values of IASL correlate with clinical test, which assess risk of falling. IASL has potential as screening tools for fear and risk of falls.