{"id":1275,"date":"2026-09-03T13:01:00","date_gmt":"2026-09-03T17:01:00","guid":{"rendered":"http:\/\/www.foxquestsystems.net\/foxblog\/?p=1275"},"modified":"2026-09-04T01:01:59","modified_gmt":"2026-09-04T05:01:59","slug":"non-overlapping-lags","status":"publish","type":"post","link":"https:\/\/www.foxquestsystems.net\/foxblog\/2026\/09\/03\/non-overlapping-lags\/","title":{"rendered":"Non-Overlapping Lags"},"content":{"rendered":"\n

In a CPM network, a lag\u2019s value should be less than the Original Duration of its predecessor and successor activity pair so that it doesn\u2019t open a gap in the flow of logic. When a lag exceeds the predecessor’s or successor’s assigned Duration, a non-overlapping condition can occur.<\/p>\n\n\n\n

Many schedule specifications prohibit using lags in place of activities. At first glance, only a Finish-to-Start relationship with a positive lag appears to break that rule (Case 2 below). On closer inspection, Cases 1, 3, and 4 break it too: any lag that opens a gap between the predecessor and successor activity pair has the same effect as the more familiar Case 2.<\/p>\n\n\n\n

These gaps are easy to create and hard to spot. A non-overlapping lag can occur in four ways and are addressed in the Z\u00fcmmer Analysis Selected Report(s) box shown in Figure 1 below:<\/p>\n\n\n

\n
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Figure 1<\/figcaption><\/figure>\n<\/div>\n\n\n

Case 1: The Negative Lag is greater than the sum of the Predecessor\u2019s Original Duration and the Successor\u2019s Original Duration (Figure 2).<\/strong><\/h2>\n\n\n\n

<\/p>\n\n\n

\n
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Figure 2<\/figcaption><\/figure>\n<\/div>\n\n\n

Suppose the Original Duration (OD) for Activities \u201cA\u201d and \u201cB\u201d are set to 5 Days each, with a Finish-To-Start (FS) relationship and a lag of -9 Days. This is an acceptable overlap, because the absolute value of the lag (9 Days) is less than the combined OD of \u201cA\u201d and \u201cB\u201d (10 Days).<\/p>\n\n\n\n

Now suppose the OD of both activities are reduced to 2 Days. Unless the relationship changes, a non-overlapping condition occurs (Figure 2): the absolute value of the FS lag (9 Days) exceeds the combined OD of \u201cA\u201d and \u201cB\u201d (4 Days), leaving a 5-Day gap between them.<\/p>\n\n\n\n

In P6, no filter can be constructed to check for this type of non-overlapping lag. Case 1 is the least common of the four, because most schedule specifications prohibit negative lags outright.<\/p>\n\n\n\n

Z\u00fcmmer<\/strong> Analysis Report #31 \u2013 \u201cNegative Lag Greater Than Sum of Both Original Durations\u201d<\/strong> flags this condition as \u201cNeg Lag > Pred OD + Succ OD.\u201d Figure 3 below lists each non-overlapping relationship as an individual pairing, showing the Activity Status and Original Duration of both the predecessor and successor, plus the relationship type and lag.<\/p>\n\n\n\n

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Figure 3<\/figcaption><\/figure>\n\n\n\n

Case 2:<\/strong> A Positive Finish-To-Start lag is used between 2 Activities (Figure 4)<\/strong>.<\/h2>\n\n\n\n

<\/p>\n\n\n

\n
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Figure 4<\/figcaption><\/figure>\n<\/div>\n\n\n

Suppose the Original Duration\n(OD) for Activities \u201cA\u201d and \u201cB\u201d are set to 7 Days each and the relationship is\nset to Finish-To-Start (FS) with a lag of -2 Days. This is overlapping since\nthe sum of the durations of \u201cA\u201d and \u201cB\u201d is 14 Days. <\/p>\n\n\n\n

Now change the lag to +7 Days. A positive Finish-To-Start lag pushes \u201cB\u201d away from \u201cA\u201d, opening a 7-Day gap. This can be resolved by replacing the lag with an activity whose Original Duration equals the lag value.<\/p>\n\n\n\n

In P6, no filter can be constructed to check for this type of non-overlapping lag. Case 2 is often used to force a successor\u2019s start date, especially when the predecessor and successor are assigned to different calendars.<\/p>\n\n\n\n

Z\u00fcmmer<\/strong> Analysis Report #32 \u2013 \u201cActivities Finish-To-Start Relationship with Positive Lag\u201d<\/strong> flags this condition as \u201cFS with Positive Lag.\u201d Figure 5 below lists each non-overlapping relationship as an individual pairing, showing the Activity Status and Original Duration of both the predecessor and successor, plus the relationship type and lag.<\/p>\n\n\n\n

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Figure 5<\/figcaption><\/figure>\n\n\n\n

Case 3:<\/strong> A Start-To-Start Lag is greater than the Predecessor\u2019s Original Duration (Figure 6).<\/strong><\/h2>\n\n\n\n

<\/p>\n\n\n

\n
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Figure 6<\/figcaption><\/figure>\n<\/div>\n\n\n

Suppose the Original Duration (OD) for Activities \u201cA\u201d and \u201cB\u201d are set to 15 Days each, with a Start-To-Start (SS) relationship and a lag of 8 Days. This is acceptable, because \u201cA\u201d and \u201cB\u201d overlap.<\/p>\n\n\n\n

Now reduce the OD of \u201cA\u201d to 5 Days. Unless the relationship changes, a non-overlapping condition occurs: the SS lag (8 Days) exceeds the OD of \u201cA\u201d (5 Days), leaving a 3-Day gap between the two activities.<\/p>\n\n\n\n

In P6, no Filter that can be\nconstructed to check for this type of Non-Overlapping Lag. <\/p>\n\n\n\n

Z\u00fcmmer<\/strong> Analysis Report #33 \u2013 \u201cStart-To-Start Relationships & Lag Greater Than Predecessor\u2019s Original Duration\u201d<\/strong> flags this condition as \u201cSS Lag > Predecessor OD.\u201d Figure 7 below lists each non-overlapping relationship as an individual pairing, showing the Activity Status and Original Duration of both the predecessor and successor, plus the relationship type and lag.<\/p>\n\n\n\n

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Figure 7<\/figcaption><\/figure>\n\n\n\n

Case 4:<\/strong> A Finish-To-Finish Lag is greater than the Successor\u2019s Original Duration (Figure 8)<\/strong>.<\/h2>\n\n\n\n

<\/p>\n\n\n

\n
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Figure 8<\/figcaption><\/figure>\n<\/div>\n\n\n

Suppose the Original Duration (OD) for Activities \u201cA\u201d and \u201cB\u201d are set to 15 Days each, with a Finish-To-Finish (FF) relationship and a lag of 8 Days. This is acceptable, because \u201cA\u201d and \u201cB\u201d overlap.<\/p>\n\n\n\n

Now reduce the OD of \u201cB\u201d to 5 Days. Unless the relationship changes, a non-overlapping condition occurs: the FF lag (8 Days) exceeds the OD of \u201cB\u201d (5 Days), leaving a 3-Day gap between the two activities.<\/p>\n\n\n\n

In P6, no Filter that can be\nconstructed to check for this type of Non-Overlapping Lag. <\/p>\n\n\n\n

Z\u00fcmmer<\/strong> Analysis Report #34 \u2013 \u201cFinish-To-Finish Relationships & Lag Greater Than Successor\u2019s Original Duration\u201d<\/strong> flags this condition as \u201cFF Lag > Successor OD.\u201d Figure 9 below lists each non-overlapping relationship as an individual pairing, showing the Activity Status and Original Duration of both the predecessor and successor, plus the relationship type and lag.<\/p>\n\n\n\n

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Figure 9<\/figcaption><\/figure>\n\n\n\n

Copyright \u00a92026 FoxQuest Systems, Inc. – All Rights Reserved<\/p>\n\n\n\n

<\/p>\n","protected":false},"excerpt":{"rendered":"

In a CPM network, a lag\u2019s value should be less than the Original Duration of its predecessor and successor activity pair so that it doesn\u2019t open a gap in the flow of logic. When a lag exceeds the predecessor’s or successor’s assigned Duration, a non-overlapping condition can occur. Many schedule specifications prohibit using lags in … Continue reading “Non-Overlapping Lags”<\/span><\/a><\/p>\n","protected":false},"author":2,"featured_media":2239,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"nf_dc_page":"","om_disable_all_campaigns":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_feature_clip_id":0,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_post_was_ever_published":false},"categories":[2],"tags":[],"class_list":["post-1275","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-analysis"],"jetpack_sharing_enabled":true,"jetpack_featured_media_url":"https:\/\/i0.wp.com\/www.foxquestsystems.net\/foxblog\/wp-content\/uploads\/2019\/10\/Feature2.png?fit=734%2C310&ssl=1","_links":{"self":[{"href":"https:\/\/www.foxquestsystems.net\/foxblog\/wp-json\/wp\/v2\/posts\/1275","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.foxquestsystems.net\/foxblog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.foxquestsystems.net\/foxblog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.foxquestsystems.net\/foxblog\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.foxquestsystems.net\/foxblog\/wp-json\/wp\/v2\/comments?post=1275"}],"version-history":[{"count":9,"href":"https:\/\/www.foxquestsystems.net\/foxblog\/wp-json\/wp\/v2\/posts\/1275\/revisions"}],"predecessor-version":[{"id":2238,"href":"https:\/\/www.foxquestsystems.net\/foxblog\/wp-json\/wp\/v2\/posts\/1275\/revisions\/2238"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.foxquestsystems.net\/foxblog\/wp-json\/wp\/v2\/media\/2239"}],"wp:attachment":[{"href":"https:\/\/www.foxquestsystems.net\/foxblog\/wp-json\/wp\/v2\/media?parent=1275"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.foxquestsystems.net\/foxblog\/wp-json\/wp\/v2\/categories?post=1275"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.foxquestsystems.net\/foxblog\/wp-json\/wp\/v2\/tags?post=1275"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}