Work, duration, and elapsed time
Accurate project planning depends on distinguishing three related but independent concepts: work, duration, and elapsed time. Raytio PPM stores all three as independent fields, giving you the flexibility to model schedules precisely.
The three concepts
Work (effort)
Work is the total effort required to complete a task, measured in person-hours (or person-days). It answers the question: "How many hours of human labour does this need?"
If a task requires 40 hours of work, that means 40 person-hours of effort regardless of how many people are assigned or how many calendar days it takes.
Duration
Duration is the number of working days a task spans on the calendar. It answers the question: "How many business days will this take?"
A task with 40 hours of work assigned to one person working 8-hour days has a duration of 5 days. The same task assigned to two people working full-time has a duration of 2.5 days — the effort is the same, but it is completed sooner.
Elapsed time
Elapsed time is the total calendar time from start to finish, including weekends, holidays, and non-working time. It answers the question: "How many calendar days between start and finish?"
A task with a 5-day duration that starts on a Monday finishes on Friday — 5 elapsed days. But a task with a 5-day duration starting on Thursday finishes the following Wednesday — 7 elapsed days (because the weekend is included in elapsed time but not in duration).
How they relate
Work, duration, and resourcing are linked by:
Duration = Work / (Units x Hours per day)
Where Units is the percentage of a resource's time allocated to the task. This means:
| Scenario | Work | Units | Duration |
|---|---|---|---|
| 1 person, full-time | 40h | 100% | 5 days |
| 2 people, full-time | 40h | 200% | 2.5 days |
| 1 person, half-time | 40h | 50% | 10 days |
| 1 person, full-time | 80h | 100% | 10 days |
Elapsed time then extends duration by accounting for non-working days:
| Duration | Start day | Elapsed days |
|---|---|---|
| 5 days | Monday | 5 |
| 5 days | Wednesday | 7 (includes weekend) |
| 10 days | Monday | 14 (includes 2 weekends) |
Storage
Each work item stores planned and actual values for work, duration, and dates independently:
| Field | Type | Purpose |
|---|---|---|
planned_work | decimal | Effort in hours |
planned_duration | decimal | Working days |
planned_start | date | Calendar start |
planned_finish | date | Calendar finish |
actual_work | decimal | Actual effort spent |
actual_duration | decimal | Actual working days |
actual_start | date | When work actually began |
actual_finish | date | When work actually completed |
Elapsed time is implicit — it is the difference between start and finish dates on the calendar.
Because the three fields are independent, you can set values that match the realities of your project without being forced into a single formula:
- A half-time task might have
planned_work = 40andplanned_duration = 10. - A concrete-curing task might have
planned_duration = 3withplanned_work = 0because no human effort is involved. - Baselines capture all fields as-is, so variance reports compare your original plan against actuals faithfully.
When to use each field
| Field | Use when |
|---|---|
| Work | You need to track effort for resource planning or cost estimation (hours x rate) |
| Duration | You need to track how long a task occupies in a Gantt chart or schedule |
| Both | You need both effort tracking and schedule tracking — most real-world tasks |
| Neither | The work item is a milestone (zero duration, zero work) or a container (epic/feature with rollup only) |
Further reading
- How PPM handles scheduling — how work, duration, and dates fit into the scheduling model
- Percent complete — manual and rollup — how progress tracking interacts with work and duration
- Baselines and variance — how planned vs actual work and duration are compared