--- title: A neat little trick with time decay | daily.dev description: A technique for computing time-decayed popularity scores without storing timestamps. Instead of tracking when each score was calculated, you factor out the... canonical: https://daily.dev/posts/a-neat-little-trick-with-time-decay-ro2uxhjvj twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: A neat little trick with time decay | daily.dev og:description: A technique for computing time-decayed popularity scores without storing timestamps. Instead of tracking when each score was calculated, you factor out the... og:url: https://daily.dev/posts/a-neat-little-trick-with-time-decay-ro2uxhjvj og:image: https://api.daily.dev/og/posts/RO2UXhjVj.png og:image:alt: A neat little trick with time decay og:image:width: 1200 og:image:height: 630 og:locale: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # A neat little trick with time decay **[Erik Bernhardsson](https://daily.dev/sources/erikbernhardsson)** · 2 min read · 0 upvotes · 0 comments ## Summary A technique for computing time-decayed popularity scores without storing timestamps. Instead of tracking when each score was calculated, you factor out the current time as a constant multiplier and store only the time-independent component. Because the raw accumulated value grows astronomically large, you store its logarithm instead. Adding new terms to a log-space sum is handled via a numerically stable log-sum-exp identity, avoiding overflow. This approach was used at Spotify for track popularity scoring. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Similar posts on daily.dev - [RAG Is Blind to Time — I Built a Temporal Layer to Fix It in Production](https://daily.dev/posts/rag-is-blind-to-time-i-built-a-temporal-layer-to-fix-it-in-production-n1qi1u6py) · Towards Data Science · 1 upvotes · 0 comments - [How YouTube Counts Millions of Live Viewers](https://daily.dev/posts/how-youtube-counts-millions-of-live-viewers-l3kj0h2bq) · Code Like A Girl · 3 upvotes · 1 comments - [Stop Treating AI Memory Like a Search Problem](https://daily.dev/posts/stop-treating-ai-memory-like-a-search-problem-iq7rmxoe7) · Towards Data Science · 1 upvotes · 0 comments - [Adding Temporal Reasoning to Graph-RAG: Tracking Fact Freshness and Staleness](https://daily.dev/posts/adding-temporal-reasoning-to-graph-rag-tracking-fact-freshness-and-staleness-iengqcl9o) · Machine Learning Mastery · 2 upvotes · 0 comments --- Tags: [#data-engineering](https://daily.dev/tags/data-engineering) [View this post on daily.dev](https://daily.dev/posts/a-neat-little-trick-with-time-decay-ro2uxhjvj) ```json {"@context":"https://schema.org","@graph":[{"@type":"Organization","@id":"https://daily.dev/#organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180},"sameAs":["https://twitter.com/dailydotdev","https://github.com/dailydotdev","https://www.linkedin.com/company/daily-dev-ltd"]},{"@type":"WebSite","@id":"https://daily.dev/#website","url":"https://daily.dev","name":"daily.dev","publisher":{"@id":"https://daily.dev/#organization"},"potentialAction":{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https://daily.dev/search?q={search_term_string}"},"query-input":"required name=search_term_string"}}]} {"@context":"https://schema.org","@type":"TechArticle","headline":"A neat little trick with time decay","url":"https://daily.dev/posts/a-neat-little-trick-with-time-decay-ro2uxhjvj","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/a-neat-little-trick-with-time-decay-ro2uxhjvj"},"datePublished":"2026-03-26T08:35:45.405Z","dateModified":"2026-03-26T08:36:46.629Z","description":"A technique for computing time-decayed popularity scores without storing timestamps. 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