Gantt charts with
critical path & AI
Critical path computed automatically. Four dependency types with lag. Saved baselines as Gantt shadows. Native .mpp import. AI risk overlay on the timeline. Not a Gantt-only tool, a full PM platform with a better Gantt.
What is the critical path?
The critical path is the sequence of dependent tasks that determines the minimum possible duration of a project. Every task on the critical path has zero float: delay any one of them by a day, and the project ends a day later. Tasks NOT on the critical path have some float, the amount of slack you can absorb without slipping the end date.
This is the single most-asked-for piece of information from a schedule. It tells you which tasks need protection (the critical ones), which can absorb re-prioritisation (the non-critical ones), and how much your end date will move if a specific task slips. Without critical path highlighting, every delay looks equally urgent. With it, the schedule sorts itself into "must finish on time" and "has room to breathe."
The math is deterministic: forward-pass through the dependency graph to compute earliest start and finish for each task, backward-pass to compute latest start and finish, then float per task = latest minus earliest. Tasks where float equals zero are critical. Most modern PM tools compute this automatically; the gap is in how clearly they surface it. Onplana highlights the critical chain across the entire Gantt and recomputes on every task or dependency change.
Six things on the Gantt
Specific capabilities, not feature-list hand-waving.
Critical path highlighted automatically
No manual flagging, the longest dependency chain (and any tied chains) is computed and highlighted across the Gantt. Re-computes on every task or dependency change. Available on every plan, including Free.
Saved baselines as Gantt shadows
Snapshot the schedule at any point, kickoff, monthly review, post-replan. The Gantt overlays planned (faded shadow) vs actual (solid bar) so slippage is visible at a glance. Multiple baselines per project; switch via dropdown.
Four dependency types with lag/lead
FS (Finish-to-Start), SS (Start-to-Start), FF (Finish-to-Finish), SF (Start-to-Finish), the four MS Project standards. Lag and lead in days, hours, or percentage. Onplana detects and refuses circular dependencies before save.
AI risk overlay on the timeline
Risk-detection suggestions surface as orange chips on the affected tasks in the Gantt. Click to see why the AI flagged it (schedule slippage, dependency cycle, resource overallocation, budget burn-rate anomaly), dismiss false positives, or accept and create a mitigation task.
Native .mpp import preserves all of the above
Drop in a .mpp from Microsoft Project; Onplana's MPXJ-based parser preserves all four dependency types with lag, milestones, ECFs, baselines, calendars. No XML conversion intermediate, no Project Desktop license needed.
Drag-and-drop scheduling, undo-safe
Drag a task to a new date; Onplana cascades dependents, refuses moves that would create cycles, and offers an undo. Drag a milestone to a new diamond position. Resize bars to change duration. Standard interactions, no surprises.
The four dependency types, with worked examples
Microsoft Project popularised the four-type dependency vocabulary; every serious scheduler since has adopted it. Lighter Gantt tools support only Finish-to-Start and silently drop the rest on import, which is where compatibility breaks. Onplana preserves all four with optional lag/lead.
Finish-to-Start
The default and most common type. Predecessor must finish before successor can start. Use for sequenced work that physically depends on the prior step.
Example: "Pour foundation" (FS) "Frame walls". You cannot frame walls before the foundation has finished curing.
Start-to-Start
Successor cannot start until predecessor starts. Use for work that runs in parallel but requires the prior task to be in motion before the next can begin.
Example: "Begin code review" (SS+1d) "Begin QA test cases". QA writes test cases while developers fix review comments, but starts a day later than review.
Finish-to-Finish
Successor cannot finish until predecessor finishes. Use for parallel work streams that must converge on a shared end date.
Example: "Code feature" (FF) "Write feature documentation". Docs can be drafted early but cannot be considered done until the feature is actually finished.
Start-to-Finish
Rarest type. Successor cannot finish until predecessor starts. Used for handoff relationships where the new role starts before the old one finishes.
Example: "Night-shift starts" (SF) "Day-shift ends". Day shift cannot end until night shift has begun, ensuring continuous coverage.
How critical path is calculated
The textbook Critical Path Method (CPM) is two passes through the dependency graph. Worth understanding even if you never look at the math, because it tells you what your scheduler is actually doing when it highlights a chain.
Forward pass: earliest start + finish
Walk the graph from the start node to every end node, computing the earliest each task can start (ES) and finish (EF). The first task starts at ES=0. Every subsequent task's ES is the maximum EF of all its predecessors plus any lag. EF = ES + duration. The longest accumulated EF at the end node is the project duration.
Backward pass: latest start + finish
Walk the graph backwards from the end node, computing the latest each task can finish (LF) and start (LS) without delaying the project. LF for the end task equals its EF (no slack at the end). For every other task, LF is the minimum LS of all its successors. LS = LF minus duration.
Float, and the critical path
For every task, total float = LS minus ES (or equivalently LF minus EF). Tasks with float = 0 are critical: any delay propagates straight to the end date. Tasks with float > 0 have slack you can absorb. The set of all zero-float tasks, traced through the dependency graph, IS the critical path.
Worked example: 4 tasks
A simple project: Design (3 days) FS Build (5 days) FS Test (2 days), with Documentation (4 days) running in parallel from Design through to Test.
| Task | Dur | ES | EF | LS | LF | Float | Critical? |
|---|---|---|---|---|---|---|---|
| Design | 3 | 0 | 3 | 0 | 3 | 0 | Yes |
| Build | 5 | 3 | 8 | 3 | 8 | 0 | Yes |
| Test | 2 | 8 | 10 | 8 | 10 | 0 | Yes |
| Docs | 4 | 3 | 7 | 6 | 10 | 3 | No (3d slack) |
Critical path: Design → Build → Test (10 days). Documentation has 3 days of float; you can start it 3 days late or extend it 3 days without slipping the end date. Onplana runs this calculation across the entire project graph on every task or dependency change and re-paints the Gantt accordingly.
Common Gantt mistakes Onplana prevents
Four specific failure modes show up in nearly every audited schedule (a pattern documented in our analysis of 500 .mpp files). Each one is a Gantt-tool design choice as much as a user error.
1Rolled-up summary dates that lie about the schedule
Many Gantt tools let you set a date on a summary task independently of its children, which silently overrides the rolled-up rollup. The summary then shows a date that has no relationship to the actual leaf-task schedule. Onplana computes summary dates from children only; the field is read-only at the summary level and the children are the source of truth.
2Critical path hidden as a colour swatch
Tools that DO compute critical path sometimes paint it as a subtle red bar indistinguishable from the default colour at small zoom levels. PMs miss it. Onplana renders critical-path tasks with a distinct outline and a dedicated legend swatch, and the critical chain stays visible at every zoom level.
3Hidden float that masks slipping tasks
When a task has float, "the schedule still ends on time" is technically true, but the float is the safety budget; consuming it without recording the consumption makes the next slip catastrophic. Onplana surfaces per-task float in the task detail panel and tracks float consumption against baseline so drift is visible early.
4Baseline drift that nobody notices
Baselines are useful only if you compare current schedule against them. Tools without first-class baseline overlay leave the comparison as a manual spreadsheet exercise nobody actually does. Onplana renders the baseline as a shadow bar behind every task on the Gantt; slippage is visible at a glance without exporting anything.
The full audit of 500 .mpp files is on the blog at We audited 500 project schedules; the patterns here are the four most common.
Onplana vs Gantt-only tools
GanttPRO, TeamGantt, Instagantt, GanttChartMaker, strong single-purpose tools. Where they end is where Onplana keeps going.
| Capability | Gantt-only tools | Onplana |
|---|---|---|
| Critical path | Often add-on or premium-tier | ✓ All plans, including Free |
| Saved baselines | Sometimes premium-tier | ✓ Multiple baselines, all plans |
| Four dependency types + lag | Often FS-only | ✓ FS / SS / FF / SF + lag/lead |
| Native .mpp import | Varies; often XML-only | ✓ Direct binary parse via MPXJ |
| AI risk detection | Not typical (single-purpose) | ✓ Continuous overlay on timeline |
| Resource pool / capacity | Limited (out of scope) | ✓ Org-wide pool + capacity heatmap |
| Stage-gate governance | Not in scope | ✓ 12-stage pipeline + multi-reviewer gates |
| Portfolio rollups | Not in scope | ✓ Multi-project RAG portfolios |
Specific Gantt-only tools vary in feature set. Use this as a category baseline rather than a per-product table, for product-specific comparisons see the dedicated /compare pages.
Try it on a real schedule
Have a Microsoft Project file? Run the free Schedule Health Check first, get an 8-point audit of critical-path bottlenecks, resource overallocation, dependency cycles, and schedule risks without signup. Then sign up free and import the same file to see it on the Gantt.
Migrating from Microsoft Project Online?
The Gantt is one piece. The full migration playbook covers exporting your data, preserving the resource model, and the September 30 2026 deadline.
Project Online migration: the complete guide
Timeline, the five real migration paths, pre-migration checklist, step-by-step process, validation. Vendor-neutral.
Read the guideHow to export Project Online data before Sept 2026
Format-by-format export playbook: project plans, resource pool, custom fields, timesheets, SharePoint. Validation + storage.
Read the playbookResource capacity planning after Project Online
Migrate the enterprise resource pool, costed timesheets, calendars, and capacity views without losing PMO rigor.
Read the guideFrequently asked questions
Does Onplana have a Gantt chart on the free plan?▾
Can the Gantt handle large schedules?▾
How does Onplana compare to dedicated Gantt tools (GanttPRO, TeamGantt, Instagantt)?▾
Does the Gantt integrate with the AI features?▾
Can I import a .mpp file and immediately see the Gantt?▾
What is the difference between critical path and longest path?▾
Does Onplana support resource-constrained critical path (CCPM)?▾
How does the Gantt handle agile sprints + traditional Gantt scheduling in the same project?▾
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