Tardiness is the amount of time a job finishes past its due date, measured as the positive gap between the planned finish and the due date. A job that finishes early or on time has zero tardiness; a job that finishes late is tardy by exactly the overrun. Total tardiness sums that lateness across every job in a plan, and weighted tardiness scales each job's lateness by its priority.
EDGEBIC by User Solutions computes tardiness as a scheduling KPI and uses it as the primary optimizer goal. This article defines the term and shows how it protects your important orders.
How It Works
Tardiness looks only at lateness. For each job, take its planned finish, subtract the due date, and if the result is positive that is the job's tardiness; if the job finishes on time or early, its tardiness is zero. It never goes negative, so finishing early does not earn credit that offsets another job's lateness. That one-sided definition is what makes tardiness a clean measure of due-date performance.
Total tardiness adds up the lateness of every job, giving a single number for the whole plan. But raw hours treat every order as equal, and orders are not equal. Weighted tardiness fixes that by multiplying each job's lateness by a priority weight, so a top-priority job counts at full weight while lower priorities count at a fraction. A plan that is a few hours late on a minor order can score better than one that is briefly late on your biggest account.
A Concrete Example
Take two work centers, a cutting station and a milling station, and three jobs released Monday morning, two of them due Tuesday at noon. Job A cuts for six hours then mills for two; Job B cuts for two hours then mills for six.
Schedule A before B and the mill sits idle all Monday morning while A's long cut blocks the saw. B cannot reach the mill until Tuesday, and it finishes two hours past its noon due date: two hours of tardiness. Now put B's short cut first. It feeds the mill by mid-morning Monday, and both jobs finish on time. Total tardiness drops from two hours to zero, purely from the sequence. Nothing was added; a machine simply stopped waiting on the wrong job.
How EDGEBIC Uses It
Tardiness is one of the KPIs the scheduling engine reports for any plan, in two forms: total tardiness in hours, and total weighted tardiness, which scales each job's lateness by one over its priority number with a small floor. The default optimizer goal, on-time first, ranks weighted tardiness ahead of everything else, so the plan it favors is the one that best protects your priority due dates.
When you run the optimizer, it searches alternative job sequences, scores each complete schedule by tardiness and the other KPIs, and shows the deltas next to your current plan. The multi-run search is clamped never worse than the plan you already had, so the tardiness it reports can only match or improve it. You review the change and accept only if it suits the week.
Tardiness pairs naturally with the delivery metrics: a plan with low weighted tardiness is what drives a strong on-time delivery rate, and it trades off against makespan when the fastest finish and the safest due dates disagree. The manufacturing glossary covers the related terms, and job shop scheduling challenges explains why lateness creeps in when jobs share machines.
Expert Q&A: Deep Dive
Q: My scheduler shows a plan with fewer late jobs, but my most important customer is one of the late ones. How do I fix that?
A: Use weighted tardiness instead of a raw late-job count. A plain count treats every late order the same, so a plan that saves two small orders by pushing your biggest account late looks like an improvement when it is not. Weighted tardiness multiplies each job's lateness by its priority, so a late high-priority order dominates the score and the optimizer will prefer a plan that protects it even at the cost of a couple of minor slips. In EDGEBIC the default on-time goal ranks weighted tardiness first, so the plan it favors is the one that keeps your priority orders on their dates.
Q: The optimizer says total tardiness dropped from three hours to zero. What did it actually change?
A: It found a job sequence that stopped a valuable machine from sitting idle behind a long operation. Tardiness is almost always caused by resources waiting on the wrong job. In a worked case, scheduling a six-hour cut before a two-hour cut left the mill idle all morning and pushed the second job two hours late. Reordering so the short cut fed the mill first cleared the idle time, and every job finished on or before its due date, dropping total tardiness from three hours to zero. Same jobs and machines, a better sequence, and the lateness simply disappeared.
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