Line-of-Balance Duration Calculator
Rhythmic flow duration with overlap and break adjustments.
Quick answer
With the default inputs: Sections m 4 strips · Processes n 3 pcs · Cycle time t 3 days etc.Total duration 18.0 days
Edit the inputs below to recalculate.Inputs
Result
Total duration
18.0days
| Base duration | 18.0days |
| Technical break | 0.0days |
| Overlap deducted | 0.0days |
| Sections m | 4strips |
| Processes n | 3pcs |
| Cycle time | 3.0days |
| Crews working at once | 3pcs |
| First section complete | 9.0days |
| Last section starts | 9.0days |
Rhythmic flow assumes every process takes the same time in every section, which rarely holds — in practice you set the cycle from the leading trade and vary crew sizes elsewhere. For multiple rhythmic flows, divide the cycle times by their greatest common divisor first; irregular flow needs the cumulative-difference method.
Reverse: known result, work out one input
Enter a target result; the other inputs stay fixed and this one is worked out.
Formula
| Rhythmic flow | T = (m + n − 1) × t |
| With breaks | T = (m + n − 1) × t + Z − C |
| Sections | m, the number of flow sections |
| Processes | n, the sequential trades |
| Cycle time | t, days one crew spends per section |
| First section | n × t |
Four sections, three processes, a 3-day cycle and no breaks: (4 + 3 − 1) × 3 = 18.0 days — the first section finishes on day 9 and the last section starts on day 9.
How to work it out
- Fix three numbers: the number of sections m (how many zones the work is split into), the number of processes n (trades in sequence) and the takt t (days per section per trade).
- For rhythmic flow the duration is T = (m + n − 1) × t. This assumes equal takt in every section and process; uneven flow needs a different method.
- Add technical delays ΣZ: concrete curing, flood testing of waterproofing and drying of plaster all take fixed time.
- Deduct overlaps ΣC where a following trade can start before the previous finishes — Blockwork can begin once the frame reaches the third floor.
- Final duration T = (m + n − 1) × t + ΣZ − ΣC, then divide by the productive-day ratio for calendar days.
Where it goes wrong
- Forgetting overlaps — frame, blockwork and plaster all overlap in practice, and ignoring that makes the programme 20-40% too long.
- Applying the rhythmic formula to uneven flow — with different takts (rebar 2 days, formwork 3, concrete 1) the formula is meaningless; use the step-and-subtract method for non-rhythmic flow.
- Setting technical delays to zero — 7-14 days of curing is hard time, and leaving it out produces a programme nobody can build.
- Swapping m and n — m is spatial sections, n is processes, and both appear in the formula, so putting them in the wrong places changes the answer.
Material and cost
The value of flow work is programme, not cost: proper flow cuts duration 30-50% against sequential working and reduces idle labour and plant, saving 10-20% of indirect cost.
On site
- Make sections roughly equal in quantity so the takts balance; uneven sections create a bottleneck and lose the benefit.
- Keep sections m at least equal to processes n, otherwise the first trade returns before finishing and there is no flow at all.
- Set the takt from the governing process — the one with most labour or the key machine — and fit the others around it.
Basis
- GB/T 50502-2009 Code for design of construction organisation
- GB 50500-2013 Code of bills of quantities and valuation for construction works
- JGJ/T 121-2015 Technical specification for network planning of construction
FAQ
Why (m + n − 1) × t rather than m × n × t?
Because overlapping is the whole point. m × n × t assumes each trade finishes a section before the next starts anywhere — no flow at all. In reality the first crew moves on and the second follows in behind, so only the first trade has a ramp-up and the last a tail, saving on the order of (n − 1) × (t − 1). The more sections, the bigger the saving over sequential working.
Is more sections always better?
No. More sections improve flow and shorten the programme, but each holds less work, crews move more often, and the face may be too small to hold a crew — efficiency drops. As a rule each section should give a crew two to three days of continuous work; below two days, mobilisation dominates and the real duration exceeds the calculation.
Why is a technical break not part of the cycle time?
Because the crew is idle during a break and produces nothing, whereas the cycle measures actual work. Folding 7 days of curing into the cycle turns a 3-day cycle into 10 and stretches the whole line; the correct treatment is a separate addition to the total, with other trades scheduled through the gap. This is why curing time dominates the programme.
Cite this page
Use this format in reports, method statements or coursework. The link is permanent.
Building Calculator. Line-of-Balance Duration Calculator. 2026-10-25. https://jianzhujisuan.com/en/schedule-flow
Results are estimating aids only and are not a design basis. Construction and final accounts must follow the drawings, the applicable standards and an approved method statement. Anything affecting structural safety, shoring or falsework must be checked by a suitably qualified engineer.