Nurse-to-Patient Ratio Modeling | Someplum Consulting

A nurse-to-patient ratio model is a unit-level calculation that compares the nursing hours a mandated ratio requires, across every shift and every day, with the nursing hours an organization can actually supply from its current and projected workforce. Its output is not a staffing schedule. It is a gap: how many funded and filled positions, by unit and by skill, sit between the mandate and reality, and what closing that gap would cost under different assumptions.

This matters now because ratio policy has moved from debate to implementation across several jurisdictions at once. Manitoba passed the first nurse-to-patient ratio legislation in Canada on June 5, 2026, with phased implementation still to be defined. British Columbia had activated ratios in roughly 73 percent of eligible units by spring 2026, with the union reporting that surge planning and cross-unit reassignment were undermining compliance in the rest. Nova Scotia is implementing ratios negotiated through collective bargaining, customized unit by unit, and slowed by existing vacancies. In the United States, unit-specific ratio bills are moving in Pennsylvania, New York, and Minnesota. Every one of these systems will be asked the same question: which units can meet the ratio on the workforce we have, and which cannot?

Ratio mandates assume a supply of nurses that constrained markets do not have. The model's job is to say, unit by unit, where that assumption holds and where it does not.

What a ratio mandate actually demands

A ratio such as 1:4 on a medical unit reads as a simple rule. Operationally it is a demand curve. The number of nurses required at any moment is the census divided by the ratio, rounded up, on every shift, including the shifts where census peaks and the shifts where two nurses call in sick. Because census varies by hour, day of week, and season, the mandate does not translate into one number of positions. It translates into a distribution of required nurses per shift, and the staffing level that satisfies the mandate on 95 percent of shifts is materially higher than the one that satisfies it on average.

Three things make this harder than it looks. First, ratios are usually defined per unit, but nurses are managed per program or per site, so the unit-level demand has to be reconciled with how staff are actually deployed. Second, mandates rarely specify what happens under surge, so organizations need a policy for the shifts the ratio cannot be met, and the model has to quantify how often that occurs. Third, the supply side is not static: attrition, retirement, leaves, and casual availability change the available hours every month, so a model that uses last year's headcount is wrong on the day it is finished.

The two sides of the model

Demand: required nursing hours by unit and shift

Required hours are derived from census, not from budgeted beds. The inputs are hourly or shift-level census by unit for at least 12 months (24 is better, to capture seasonality), the mandated ratio for that unit type, and the rules for how the ratio applies to charge nurses, breaks, admissions, and transfers. The output is a required-nurses-per-shift series and, from it, the annual required productive hours at whatever compliance threshold leadership chooses.

Supply: available nursing hours by unit and skill

Available hours are derived from the funded and filled positions on the unit, converted to productive hours after vacation, sick time, education, and orientation, then adjusted for the flows that change them: hires in the pipeline, projected retirements, attrition by tenure band, leaves, and the realistic contribution of casual and float staff. This is the same stock-flow structure used in health workforce forecasting generally, applied at unit resolution.

Building the model: seven steps

Define the unit list and ratio rules

Map every in-scope unit to its mandated ratio and to the rules that modify it (charge nurse exclusions, break coverage, pediatric and ICU acuity variants). Where the mandate is silent, document the interpretation and have nursing leadership sign it.

Assemble census at shift resolution

Pull midnight census plus admissions, discharges, and transfers by hour, or use ADT timestamps to reconstruct hourly occupancy. Twelve months minimum. Flag units that were reconfigured mid-year.

Compute required nurses per shift

Census divided by ratio, rounded up, per shift, per day. Produce the distribution, not the mean. Decide the compliance threshold (for example, meet the ratio on 95 percent of shifts) explicitly.

Build the supply baseline

Funded FTE, filled FTE, and vacancy by unit and classification. Convert to productive hours using unit-level actuals. Include casual and float contribution as a measured average, not an assumption.

Project supply forward

Apply attrition by tenure band, projected retirements from age profile, hiring pipeline with realistic time-to-fill and time-to-independence, and known leaves. Twelve to 36 months.

Quantify the gap and price the options

Gap in hours, converted to FTE and to dollars, per unit, per quarter. Then model the levers: internal float pool, changed skill mix where the mandate allows, recruitment at achievable rates, agency at current rates, and phased activation by unit.

Sequence implementation

Rank units by feasibility (smallest gap relative to supply) and by risk. The output is a phased plan that activates units in an order the workforce can support, with a dated trigger for each.

What the model tells leadership that a staffing plan cannot

Which units can be activated now, which need a defined number of hires first, and which cannot meet the ratio at any achievable recruitment rate without changing the model of care.
The real cost of the mandate under the organization's own supply, rather than the provincial or state estimate, and how much of that cost is avoidable through float capacity versus agency.
How often surge will breach the ratio even at full staffing, which is the number needed for the surge policy and for the conversation with the union.
Where cross-unit reassignment (the practice BC nurses flagged as breaking compliance) is a symptom of a structural gap on the sending unit rather than a management choice.

Common failures

Modeling to budgeted beds instead of census. Budgeted beds understate peak demand and overstate compliance.
Using one productive-hours factor system-wide. Units differ by ten points or more.
Treating vacancies as fillable at posted rates. Time-to-fill and time-to-independence for specialty units are frequently six to twelve months; the model must use the organization's own history.
Building it once. Supply changes monthly. A model nobody maintains is a report, not a planning tool. The reporting foundation (definitions, pipelines, refresh cadence) is what makes it durable.

Sources

Government of Manitoba. Manitoba Government Passes Nurse-to-Patient Ratios Legislation. June 5, 2026. news.gov.mb.ca
PressProgress. Three Canadian Provinces are on Board with Minimum Nurse-to-Patient Ratios. April 2026. pressprogress.ca
BC Nurses' Union. Minimum Nurse-to-Patient Ratios. bcnu.org
Health Workforce Canada. State of Health Workforce Modelling and Forecasting in Canada. 2024. healthworkforce.ca
Aiken, L. et al. Policies to Achieve Hospital Nurse Staffing Adequacy. AFT Health Care, Fall 2025. aft.org

Questions leaders ask about ratio modeling

How long does a ratio feasibility model take to build?

For a health authority with usable census and HR data, a first version covering all in-scope units typically takes four to eight weeks. Most of that time goes to reconciling unit definitions between the clinical, HR, and scheduling systems rather than to the arithmetic.

Do we need a workforce management or scheduling system in place first?

No. The model needs census, positions, and productive-hours actuals. Those exist in ADT, HR, and payroll systems regardless of scheduling platform. A scheduling system makes the supply side more precise and makes the model easier to maintain.

What is the difference between this and a staffing plan?

A staffing plan sets the target for a unit. A ratio model tests whether the target is achievable with the workforce the organization will actually have, when, and at what cost. It is the step before the staffing plan that most organizations skip.

Can the model be used in bargaining or in a legislative submission?

Yes, and that is often its highest-value use. Because every assumption is documented and validated against actuals, the output is defensible in front of a union, a ministry, or an auditor.

Modeling Nurse-to-Patient Ratios: What a Mandate Costs Under Real Supply