How is per-diem billing calculated for each investigator?

Per-diem charges are calculated as: cage count $\times$ per-diem rate $\times$ number of days in the billing period. This is the base charge for housing animals. Additional service charges (genotyping, breeding, surgery) are added on top.

What are tier discounts in vivarium billing?

Tier discounts reward high-volume users. For example, investigators with 50+ cages might get 5% off, and those with 100+ cages get 10% off. Discounts are applied to the gross total before cost-share adjustments.

How do faculty startup credits work?

New faculty often receive startup funds that include vivarium credits. These credits are applied after all other discounts (tier and cost-share) to reduce the final bill. Unused credits roll over to subsequent billing periods until exhausted.

What is cost-share billing?

Cost-share arrangements subsidize a percentage of an investigator's vivarium costs, typically funded by the department, center, or institutional funds. A 50% cost-share means the PI pays half and the institution covers the rest.

ToolsConductScience tool

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Per-Investigator Billing Calculator.

Compute per-PI vivarium charges from cage census, service usage, and per-diem rates with tier discounts, cost-share, and startup credits.

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Validated2026-04-08

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Billing Settings

Per-diem rate ($/cage/day) *

Billing start *

Billing end *

Tier discount

Service Rates

Service name

Rate per unit ($)

Investigators

Name *

Department

Cages

Cost-share %

Startup credit ($)

Required fields

Investigator 1: name is required.
Service rate 1: name is required.
Billing period start date must be YYYY-MM-DD format.
Billing period end date must be YYYY-MM-DD format.

When to use

Monthly or quarterly vivarium billing reconciliation
Forecasting per-PI costs for grant budgets
Evaluating tier discount impact on facility revenue
Generating per-PI invoices with service breakdowns

Do not use for

Setting per-diem rates (use Recharge Rate Calculator)
Facility-wide space allocation (use Vivarium Space Planner)
Grant-level budget planning (use NIH Animal Cost Budget Calculator)

Pearl

Run billing projections before the billing period closes to catch census discrepancies. PIs often dispute charges when the bill arrives — having real-time projections prevents surprises.

Pearl

Apply tier discounts before cost-share calculations. This ensures the institution subsidy covers the discounted rate, not the full rate.

Pitfall

Do not include startup credits in recharge rate calculations. Credits represent a temporary subsidy, not a permanent reduction in operating costs.

Pitfall

Service rates must cover actual costs (equipment, reagents, labor). Under-pricing services to attract users can create a structural deficit that per-diem increases alone cannot fix.

Method

For each investigator: gross charges = (cage count $\times$ per-diem rate $\times$ billing days) + sum(service units $\times$ service rates). Tier discounts are applied based on cage count thresholds. Cost-share percentage is applied to the post-discount amount. Startup credits are deducted last, capped at the remaining balance. Facility revenue is the sum of all net totals.

Validated

Last validated 2026-04-08. Calculations are designed for planning and documentation support; verify procurement decisions against manufacturer specifications or institutional SOPs.

How to cite

How to Cite

ConductScience Per-Investigator Billing Calculator (v1.27.0). ConductScience. https://conductscience.com/tools/per-investigator-billing-calculator

OMB Uniform Guidance, 2 CFR Part 200: Cost Principles for Federal Awards.

Vivarium Billing Models for Core Facilities

Core facility vivarium billing involves several components:

Per-diem charges: The base daily rate per cage covers animal housing, husbandry, food, bedding, and environmental monitoring. Rates vary by species and cage type (standard, IVC, metabolic, large animal).

Service charges: Specialized services like genotyping, colony breeding management, surgical procedures, and health monitoring are billed separately at per-unit rates.

Tier discounts: High-volume investigators often receive graduated discounts to incentivize facility utilization and ensure fixed costs are distributed across a larger census.

Subsidies and credits: Faculty startup packages, department cost-share agreements, and institutional subsidies reduce the PI's out-of-pocket costs. These must be tracked and reconciled against funding sources.

Billing reconciliation: Monthly or quarterly billing cycles require cage census snapshots, service logs, and discount calculations for each PI. Discrepancies between projected and actual census are common pain points.

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Per-Investigator Billing Calculator.

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Billing Settings

Service Rates

Investigators

Pearl

Pearl

Pitfall

Pitfall

Method

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How to cite

How to Cite

Vivarium Billing Models for Core Facilities

Frequently asked

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ConductColony

Per-Diem Billing Generator

Recharge Rate Calculator

Allocation & Quota Planner