Why do IT projects overrun deadlines?

IT projects overrun mainly because the capacity actually available is lower than the capacity the plan was built on: leave and run work not deducted, too many parallel projects on the same people, biased estimates, and poorly anticipated dependencies. Fixing capacity (measuring it net, limiting work in progress) works more reliably than lengthening schedules.

Why do my IT projects overrun deadlines?

Most of the time the problem is capacity, not task estimation.

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The six most frequent causes

  • Gross capacity used instead of net capacity (leave, run work, and meetings forgotten).
  • Multitasking: too many parallel projects, so lead times grow (Little's law).
  • Hidden overload: one person planned above 100% across several projects.
  • Unpredictable run work interrupting projects.
  • Optimistic estimates never compared with actuals.
  • Cross-team dependencies delaying milestones.

How to diagnose

  • Compute allocation rate per person and per team over the next three months.
  • Compare planned and actual on the latest completed projects.
  • Count active projects per team and the real run share.
  • Spot the resource that appears in the most late projects.

Concrete remedies

  • Plan on net capacity, with a measured focus factor.
  • Limit the number of active projects per team.
  • Protect scarce experts and lift the constraint (theory of constraints).
  • Re-estimate from planned vs actual rather than reusing optimistic figures.

FAQ

Is it always a capacity problem?

No, but it is the most frequent one. Dependencies, shifting scope, and estimate quality also play a role; planned vs actual helps tell them apart.

Is lengthening deadlines enough?

Rarely: without acting on capacity or the number of parallel projects, the delay repeats on the next project.

Which indicator should you track first?

Allocation rate per team: above 100%, delays are likely.

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