In simultaneous interpreting, the rate of source speech (SR) plays an important role in the quality of the interpreter. As the rate of speech increases, interpreters have to process and translate words faster, which can lead to more errors. This phenomenon is because faster speech harms the interpreter's attention and work, causing more omissions, additions, and other linguistic and paralinguistic errors. The impact of these errors can affect the accuracy and quality of interpretation, which highlights the need to understand how changes in speech rate affect performance and the production of good strategies to solve problems. This study examines how the rate of speech (SR) affects the quality of simultaneous interpreting (SI), particularly to assess the impact of the rate of speech on the interpreter. For this purpose, a method was adopted that was divided into seven categories based on Barik's (1971) classification. These categories include segment omission, word and phrase-level omission, deviation of meaning, addition, incomplete sentence, full pause, and long pause. In this study, the performance of six United Nations interpreters with many years of experience was evaluated using six audios ranging from 124 to 164 words per minute (wpm). Findings indicated that higher speaking frequency led to more errors, especially in word and segment omissions. This emphasizes the importance of addressing specific strategies to overcome the challenges that rapid speech can pose to the accuracy and effectiveness of simultaneous interpreting.