--- title: Why software projects take longer than you think: a... description: Software estimation is systematically biased because developers estimate the median completion time well, but the mean is far higher due to the log-normal... canonical: https://daily.dev/posts/why-software-projects-take-longer-than-you-think-a-statistical-model-rll4oyh9r twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: Why software projects take longer than you think: a statistical model | daily.dev og:description: Software estimation is systematically biased because developers estimate the median completion time well, but the mean is far higher due to the log-normal... og:url: https://daily.dev/posts/why-software-projects-take-longer-than-you-think-a-statistical-model-rll4oyh9r og:image: https://api.daily.dev/og/posts/Rll4OyH9r.png og:image:alt: Why software projects take longer than you think: a statistical model 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. # Why software projects take longer than you think: a statistical model **[Erik Bernhardsson](https://daily.dev/sources/erikbernhardsson)** · 9 min read · 0 upvotes · 0 comments ## Summary Software estimation is systematically biased because developers estimate the median completion time well, but the mean is far higher due to the log-normal distribution of actual vs. estimated time. Using empirical data, the median blowup factor is exactly 1x while the mean is 1.81x. When summing multiple tasks, high-uncertainty tasks dominate the total time — a single task with σ=2 can dwarf all others combined. Fitting a Student's t-distribution to real project data reveals that the 99th percentile blowup is 32x, and the theoretical mean blowup factor for any unknown task is actually infinite. The practical takeaway: instead of summing estimates, identify and focus on the highest-uncertainty tasks, as they will dominate delivery timelines. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Similar posts on daily.dev - [How to Estimate the Duration of a Task](https://daily.dev/posts/how-to-estimate-the-duration-of-a-task-ynbcs3xgt) · The Polymathic Engineer · 30 upvotes · 1 comments - [Why Is Everything in Software Always 90% Done?](https://daily.dev/posts/why-is-everything-in-software-always-90-done--bwqukhza4) · Medium · 0 upvotes · 0 comments - [How I estimate work as a staff software engineer](https://daily.dev/posts/how-i-estimate-work-as-a-staff-software-engineer-vte4dhynt) · Lobsters · 0 upvotes · 0 comments - [Estimates – a necessary evil?](https://daily.dev/posts/estimates-a-necessary-evil--ajvavuowp) · Hacker News · 0 upvotes · 0 comments --- Tags: [#statistics](https://daily.dev/tags/statistics) [View this post on daily.dev](https://daily.dev/posts/why-software-projects-take-longer-than-you-think-a-statistical-model-rll4oyh9r) ```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":"Why software projects take longer than you think: a statistical model","url":"https://daily.dev/posts/why-software-projects-take-longer-than-you-think-a-statistical-model-rll4oyh9r","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/why-software-projects-take-longer-than-you-think-a-statistical-model-rll4oyh9r"},"datePublished":"2026-03-26T08:35:15.793Z","dateModified":"2026-03-26T08:37:53.749Z","description":"Software estimation is systematically biased because developers estimate the median completion time well, but the mean is far higher due to the log-normal...","image":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/cb98a5473189c050ae3e15bd43429902?_a=AQAEuop","thumbnailUrl":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/cb98a5473189c050ae3e15bd43429902?_a=AQAEuop","isAccessibleForFree":true,"articleSection":"Erik Bernhardsson","inLanguage":"en","publisher":{"@type":"Organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180}},"author":{"@type":"Organization","name":"Erik Bernhardsson","logo":"https://media.daily.dev/image/upload/s--SlM88DTW--/f_auto,q_auto/v1774514112/logos/erikbernhardsson?_a=BAMAMiWQ0","url":"https://daily.dev/sources/erikbernhardsson"},"commentCount":0,"discussionUrl":"https://daily.dev/posts/why-software-projects-take-longer-than-you-think-a-statistical-model-rll4oyh9r","interactionStatistic":[{"@type":"InteractionCounter","interactionType":{"@type":"LikeAction"},"userInteractionCount":0},{"@type":"InteractionCounter","interactionType":{"@type":"CommentAction"},"userInteractionCount":0}],"keywords":"statistics","timeRequired":"PT9M"} {"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https://daily.dev"},{"@type":"ListItem","position":2,"name":"Erik Bernhardsson","item":"https://daily.dev/sources/erikbernhardsson"},{"@type":"ListItem","position":3,"name":"Why software projects take longer than you think: a statistical model"}]} ```