As announced in the [previous survey](https://atcoder.jp/contests/ahc-survey2024), we will update the AHC rating calculation formula starting in 2025. For detailed information about the formula, please refer to [this document](https://img.atcoder.jp/file/AHC_rating_v2_en.pdf). ### Changes 1. Time decay will be introduced to ratings. 2. Weighting will be applied to contests. ### About Time Decay Under the current system, a performance value is assigned for each contest result, and ratings are derived from the cumulative performance values obtained. Under the new rating system, the performance values will decay over time based on the number of days since the contest ended. This change will make recent contest results more impactful on ratings compared to older ones. ### About Weighting In 2025, we aim to host six long contests and 12 short contests. If the current rating formula were applied as is, the influence of short contests on ratings would become disproportionately large. To address this, we will set the weight for long contests in 2025 to **1**, and for short contests to **0.5**. For example, earning a performance value of **p** in a single contest with a weight of 1 will have the same contribution to the rating as earning **p** twice in contests with a weight of 0.5. From 2026 onward, we plan to adjust the weights to ensure that the total annual weight for long contests and short contests remains roughly equal. For contests held in 2024 and earlier, where the number of long and short contests was approximately the same, all weights will be set to **1**. ### Transition to the New Rating Before the first contest of the new year, AHC041, we will recalculate all users' ratings using the new formula. Historical contest results will remain unchanged, but current ratings will be updated accordingly. (Updated on 1/17) The transition to the new rating system has been completed. Please note that since the highest rating is updated only after participating in a contest, the rating at the time of transition will not be reflected in the highest rating. Thank you for your understanding.