Aims: To describe acute hearing threshold shifts during cisplatin-based concurrent chemoradiotherapy (CCRT) and to estimate progression to clinically relevant speech-frequency hearing loss. Methodology: We reviewed patients treated with cisplatin (up to three cycles) plus radiotherapy (70 Gy/35 fractions, 2 Gy/fraction) from April 2014 to December 2025. Audiometry (125-8000 Hz) was obtained pre-treatment, before each cycle, and 1 week after each cycle. Ears with other-cause hearing loss were excluded. Mean cochlear delivered/planned dose was available only for volumetric modulated arc therapy (VMAT) plans; planned dose was used. Inter-ear correlation was handled with linear mixed-effects models (random patient intercept). Results: In 163 patients (311 ears), final threshold increases were greatest at high frequencies (4 kHz +11 dB; 8 kHz +21 dB). Acute 8-kHz shifts occurred within 1 week after each cycle: +10.7 dB (cycle 1), +8.9 dB (cycle 2), and +4.8 dB (cycle 3). Acute shift was larger when pre-cycle 8-kHz threshold was <50 dB than >=50 dB (cycle 1: +16.1 vs +2.9 dB; p<0.001), consistent with a ceiling effect near 50 dB HL. Progression to WHO-defined moderate hearing loss based on better-ear pure-tone average across 0.5, 1, 2, and 4 kHz (PTA4) >=40 dB occurred in 30.2% of patients with baseline mild hearing loss (PTA4 25-<40 dB) versus 3.7% with normal baseline hearing (PTA4 <25 dB). Conclusion: Cisplatin CCRT causes rapid, predominantly high-frequency deterioration after each cycle and shows a ceiling effect near 50 dB HL. In contrast, clinically actionable speech-frequency moderate hearing loss is mainly observed in patients with pre-treatment mild hearing loss, supporting baseline PTA4 stratification for counseling and follow-up. Conflicts of interest: None.