Balance constraints and uncertainty

What you will understand

• Distinguish an estimate from a target and a tolerance.
• Recognise dependencies and resource constraints in a plan.
• Consider all seven performance aspects when evaluating a trade-off.

The idea

A target says what we are trying to achieve. An estimate says what the evidence suggests is likely. A tolerance says how much variation is allowed before a higher level must decide. Confusing these ideas creates plans that look certain but cannot support honest control. Good planning makes constraints and uncertainty visible while there is still time to respond.

Estimates should draw on relevant experience, specialist judgement and the characteristics of the work. Record the assumptions and consider a range where uncertainty warrants it. Effort and duration are different: a task requiring five person-days may take longer than five calendar days if the specialist is available only part time. Adding people does not always shorten work proportionately, especially where handovers or a sequential dependency limit progress.

A dependency means that one element relies on another. Some are internal to the project; others depend on suppliers, business decisions, external approvals or operations. A resource constraint arises when required capacity is unavailable, even if the logical sequence would allow work to proceed. A schedule should account for both. Two independent tests still cannot run at the same time if there is only one suitable testing facility.

Tolerances create delegated flexibility around agreed targets. Version 7 considers benefits, cost, time, quality, scope, risk and sustainability. A stage finishing within its time tolerance can still require escalation if its forecast exceeds an agreed cost or sustainability tolerance. A manager does not own unrestricted authority simply because one measure remains healthy. The applicable tolerances and decision rights must be explicitly agreed.

Constraints interact. Accelerating delivery could increase cost, reduce a benefit or increase waste. A smaller scope could protect a deadline but remove the feature that makes the investment worthwhile. Assess the effect on the business case and agreed performance aspects before deciding. Tailored controls may express scope flexibility through prioritised requirements, but protected requirements and acceptance obligations cannot be quietly discarded to make a forecast look better.

The planning horizon and management stages help handle uncertainty without losing a whole-project perspective. Detail the work that can be forecast responsibly, identify assumptions about later work and revisit them at suitable points. Include the management and quality activities needed for delivery, not just construction tasks. A credible plan explains the resources, constraints, sustainability implications and controls supporting its dates, and distinguishes an agreed reserve or budget from an unsupported promise that nothing will go wrong.

A schedule is a reasoned forecast

Points to remember

• Effort, elapsed duration, target and tolerance describe different things.
• Resources can constrain a schedule even without a logical dependency.
• Sustainability is one of the seven performance aspects.

Your takeaway

Useful plans expose assumptions and consider realistic resources, dependencies and uncertainty. Evaluate trade-offs against all relevant tolerances and the business case rather than optimising a single target in isolation.