Birth intervals, the time duration between consecutive births, hold significance in demographic studies and family planning research. Two common approaches for measuring birth intervals are the "Usual Closed" and "Most Recent Closed" methods. This study investigates the differences between these two approaches and their implications for demographic analyses. Through an analysis of birth interval data, we compare the results obtained using these methods, examining their strengths, limitations, and potential impacts on fertility and family planning programs. This research sheds light on the importance of choosing an appropriate birth interval definition in demographic studies.