How I’d actually use this on a flip
I size the construction loan against this number, not the median. The lender wants a finish date; the project wants a buffer; the calc gives me both. On a Chicago-metro gut rehab at 2000 sqft, typical permit, moderate complexity, GC-managed — the median horizon is roughly eight months, and the buffered ceiling adds another five to seven weeks for inspection re-dos and the cabinet maker who blocked another GC’s order ahead of mine. I always quote the lender the buffered ceiling and explain the 15-20% cushion in the same sentence as the loan term.
The owner-builder toggle is the one I run twice on every deal. If the calc says nine months GC-managed and eleven months owner-builder, the question I ask myself isn’t “can I save the GC markup” — it’s “is the construction loan term long enough to absorb the 1.26x slowdown and still service rate-and-term?” The Census 2024 anchor is exactly that: 12.1 months contractor versus 15.2 months owner-builder for new construction. The calc applies the same ratio to the rehab durations because the math behind the slowdown is coordination overhead, not slower trades.
Permit jurisdiction is the third pass. A 1920s Chicago bungalow in a fast-jurisdiction suburb clears plans in two weeks and breaks ground inside a month. The same property in a slow Cook-County jurisdiction with a structural-review department reviewing every joist size loses six weeks of construction-loan term to plan revisions before demo starts. The calc surfaces the difference; the pre-offer walk-through is when I check which jurisdiction the property sits in.
Where the schedule actually breaks
Five places the timeline lies to operators who don’t know to look — exactly where the calc’s critical path and delay-risk notes are pointed:
- Permit revisions.The first plan submission rarely clears. The second often doesn’t either. Strict jurisdictions queue revisions in two-week increments; on a schedule that already counts permits at five weeks, two revisions is ten weeks of construction-loan time before a single line of demo paint comes off. If the deal pencils only with a one-revision assumption, the deal doesn’t pencil.
- Rough-in inspection slip.All three rough trades — electrical, plumbing, HVAC — converge on a single inspection gate. If any one of them misses the gate, the entire project sits while that trade reschedules. Plan a one-week reinspection buffer; that’s where projects pick up their first real slip. The calc surfaces this on the rough-inspection delay-risk note.
- Cabinet + counter lead time.The two-week counter-fab window after templating isn’t a phase you can compress; it’s a supplier lead time you eat in calendar days regardless of how fast your install crew moves. Order cabinets the day permits clear or you’re paying for the lead time at the wrong end of the project — when you’re trying to call the final inspection.
- Drywall finish quality vs schedule pace.Drywall is the longest single phase on a residential rehab. Hang + tape + 5-coat finish + sand on 2000 sqft is four weeks at full crew. Owner-builder pace stretches that to five or six because the best mudders don’t run their best crews on owner-managed jobs. If the calc’s OB total feels wrong, it’s usually drywall pulling the slowdown.
- Final inspection forgotten items.Final failure on a forgotten smoke detector or an unrated dryer vent costs a two-week reinspection slot — and the punch-list phase can’t close out until the certificate of occupancy lands. Walk the punch list with the inspector’s checklist a week before you call. The calc hard-codes a three-day inspection block; the slip is what the buffer is for.
Methodology
Every day count on this page traces to one of three layers: Census 2024 single-family build-duration anchors, SiteworkMath phase calibrations from flipper experience + AIA contract cadences, and standard CPM forward + backward pass for critical-path identification. The full per-calculator sourcing tier in methodology spells out which sources back which kinds of claims. The output is a planning horizon, not a contractor schedule — the schedule caveat is part of the engine output for a reason.
Show the formulas
- Per-phase duration:
baseDays × sqftFactor × permitFactor × obFactor × complexityFactorwith each factor applied per the phase’s response setting (full / partial / none). - Sqft scaling (sublinear):
(sqft / 2000) ^ 0.7. Doubling sqft adds about 62%, not 100% — crews flex with project size. - Permit jurisdiction multiplier: fast 0.4× (small Chicago suburbs) / typical 1.0× (most Chicago metro) / slow 2.5× (Cook County strict). Applies fully to permit review; partially to design + final inspection.
- Owner-builder multiplier: 1.26× on coordination phases — anchored on Census 2024 single-family build durations (15.2mo OB / 12.1mo contractor). Inspections and design are unaffected.
- Complexity multiplier: simple 0.85× / moderate 1.0× / complex 1.18×.
- Critical path:forward pass establishes earliest start + finish from predecessors; backward pass from successors establishes latest start + finish; phases with float < 0.5 day are critical.
- Buffer: 15% on simple / 17.5% on moderate / 20% on complex — applied to the critical-path total to produce the bufferedTotalDays ceiling.
- Engine logic:
lib/sitework/timeline/timeline.tswith phase catalog inphases.tsand types intypes.ts. Tested intimeline.test.ts.
Frequently asked
What does this construction timeline calculator estimate?
A planning-range schedule for a residential renovation or new build — the calendar-day total you'd use to test whether a contractor's timeline, a move-in date, or a construction-loan term is realistic. Not a contractor schedule. What the engine does: Walks through roughly 20 phases of a real project — design, permit review, demo or site prep, structure, envelope, rough trades, inspections, drywall, finishes, punch list — and tracks which phases depend on which others. It then identifies the chain of phases that drives the finish date. What the output shows: A median calendar-day total plus a buffered ceiling for slip days. The buffer covers things that aren't tied to one phase — inspection re-dos, weather, a supplier that ghosts your order.
Why is owner-builder slower than contractor-managed?
1.26× slower on average. Single-family contractor-built homes average 12.1 months from start to completion; owner-built run 15.2 months, per the most recent US Census Survey of Construction data. Why the slowdown happens: Coordination overhead, not the subs running slower. A single owner running 8 trades has gaps in the schedule that a GC's superintendent fills automatically. Where the multiplier applies: Coordination-heavy phases — rough trades, finishes, drywall. Where it doesn't apply: Inspection wait times and design phases. Those move at the same pace regardless of who's managing the job.
How does the permit jurisdiction tier change the schedule?
Permits are calendar risk, not just fees. The three tiers change how long plan review takes — fast offices clear in 1–2 weeks, slow ones can take 10+ weeks plus a revision cycle. Fast: Small Chicago suburbs and contractor-friendly municipal review. Typical: Most of the Chicago metro. About 5 weeks. Slow: Cook County strict review or jurisdictions with a structural review department. 10–12 weeks plus a third revision cycle is routine. Why this matters financially: Strict-jurisdiction risk doesn't just delay the project — it eats construction-loan term while the calendar burns. The methodology section shows the per-phase multiplier.
What's the critical path?
The chain of phases where any delay pushes the finish date out by the same amount. If permit review is on the critical path and slips a week, the whole project slips a week. Phases off the critical path have some slack — they can slip without moving the date. The usual critical path on a gut rehab: design → permits → demo → framing → trade rough-in → rough inspection → drywall → finishes → final inspection → punch list. What runs in parallel with slack: Windows and doors, tile prep, and similar trades run alongside the main spine. They can slip a few days without moving the finish date — but if they slip too far, they jump onto the critical path and start dragging the project. Where it shows on the Gantt: The critical-path bars are outlined so you can see at a glance which phases need the most protection.
How accurate is this calculator's output?
Planning range, not a contractor schedule. Use it to decide whether the project's pace pencils before booking the GC. Where phase durations come from: Site calibrations anchored on US Census single-family build-duration data and standard contract cadences, cross-checked with the national cost-guide aggregators and overlaid with Chicago-metro flipper experience. How sqft scales: Sub-linear (raised to the 0.7 power), because crews flex with project size. A 4,000 sq ft project doesn't take 2× the time of a 2,000 sq ft project — it takes about 1.6×. What the buffer covers: 15-20% on the ceiling absorbs inspection re-dos, weather windows, and supplier ghost-jobs that aren't directly on any single phase. Where the dollar side lives: The gut-rehab cost calculator next door surfaces the same project decision from the budget side.
What I’d do next
- Pair the schedule with the cost — gut rehab cost calc
The same project decision has two halves: dollars and calendar. Run the cost calc with matching inputs to surface the feasibility budget alongside this schedule horizon.
- Read the planning-range methodology
What's anchored on Census 2024, what's a SiteworkMath calibration, and how the buffer cushion is sized.
- Refine the foundation-work line — concrete yardage calc
If foundation work is in scope (and adds the foundation phase to the timeline), drop into the concrete calc to size the slab / footing / pier order.
By James Wu. Planning-range methodology and per-calculator sourcing tiers in methodology. Owner-builder slowdown anchored on US Census 2024 Survey of Construction (single-family build durations: contractor 12.1mo / owner-builder 15.2mo → 1.26x). Phase durations are SiteworkMath calibrations anchored on flipper experience + AIA contract cadences + HomeAdvisor / Fixr cross-checks. Critical path computed via standard forward + backward CPM pass. Engine logic in lib/sitework/timeline/timeline.ts. Numbers are SiteworkMath planning ranges, not contractor schedules — the schedule caveat is part of the output for that reason. Not structural, financial, or legal advice. Full methodology.