projectionmodels 0.6.1

Focused actuarial claim, premium, membership, and expense projections.

projectionmodels

Focused actuarial projections of claims, premium, and expenses on supplied exposure.

The package is intentionally organized around concrete workflows. Most users should not need to construct a calculation graph or define a custom state engine.

Installation

pip install projectionmodels

projectionmodels currently supports actuarialpy>=0.41,<0.45 and Python 3.10–3.13.

Public API

The package root contains the workflow objects most actuaries need:

ClaimExperience        Prepare a base claim rate from experience
ClaimProjection        Project claim rates and claims by claim type
PremiumProjection      Roll premium forward, including renewal rate actions
RenewalRateActions     Supply effective-dated rate actions
ExpenseProjection      Project per-exposure, fixed, premium-based, and claim-based expenses
ProjectionHorizon      Define monthly, quarterly, or annual projection periods
ProjectionDates        Define entry, exit, renewal, and experience date columns
DateCohort              Split records into existing/new or other date cohorts
Adjustment / Scenario  Run sensitivities and alternative assumptions
ProjectionResults      Summarize without averaging ratios or duplicating exposure

Lower-level modeling objects are available from projectionmodels.advanced, but they are not part of the primary workflow.

Premium at renewal

import pandas as pd
import projectionmodels as pm

premium_data = pd.DataFrame(
    {
        "group_id": ["A", "B"],
        "renewal_date": pd.to_datetime(["2027-03-01", "2027-07-01"]),
        "current_premium_rate": [100.0, 100.0],
        "rate_action": [0.10, 0.20],
    }
)

periods = pd.period_range("2027-01", periods=12, freq="M").astype(str)
exposure = pd.DataFrame(
    [
        {
            "group_id": group_id,
            "projection_period": period,
            "member_months": 1_000.0,
        }
        for group_id in ("A", "B")
        for period in periods
    ]
)

results = pm.PremiumProjection(
    premium_data=premium_data,
    projection_keys=["group_id"],
    exposure=exposure,
    exposure_col="member_months",
    horizon=pm.ProjectionHorizon("2027-01-01", periods=12),
    recurring_rate_action_col="rate_action",
).project()

Group A remains at $100 through February, increases to $110 in March, and carries that rate forward. Group B increases to $120 in July.

For different actions at different renewals, provide an effective-dated table:

actions = pm.RenewalRateActions(
    pd.DataFrame(
        {
            "group_id": ["A", "A", "B"],
            "effective_date": pd.to_datetime(
                ["2027-03-01", "2028-03-01", "2027-07-01"]
            ),
            "rate_action": [0.10, 0.06, 0.20],
        }
    ),
    projection_keys=["group_id"],
)

Claims by claim type

experience = pm.ClaimExperience(
    claims,
    projection_keys=["group_id", "product_id"],
    claim_type_col="claim_type",
    date_col="incurred_month",
    claims_col="reported_claims",
    exposure_col="member_months",
    valuation_date="2026-12-31",
)

projection = pm.ClaimProjection.from_experience(
    experience,
    exposure=exposure,
    exposure_col="member_months",
    horizon=pm.ProjectionHorizon("2027-01-01", periods=36),
    completion=completion,
    trend=trend,
    seasonality=seasonality,
    credibility=credibility,
    complement=manual_rates,
)

results = projection.project()

Trend, seasonality, completion, and credibility may be supplied directly as assumption tables.

Cost levels and pipeline order

The claim workflow evaluates, in order: complete → deseasonalize → trend the experience rate to the blend basis → credibility blend → trend from the basis to each projection period → reseasonalize → add rate_loads → multiply by exposure. Exposure is whatever unit the book uses — member-months, policy months, car-years — named with exposure_col.

The complement is used as stated. By default the blend basis is the prospective midpoint of the horizon (complement_basis="prospective"), the level at which manual and book rates are conventionally quoted — so a zero-credibility projection reproduces the complement rather than a trended copy of it. Set complement_basis="experience" if your complement is quoted at experience-period cost level, or pass an explicit as-of date. Because the month arithmetic is exactly additive, results at full credibility are identical under every basis.

rate_loads (for example a pooling charge) are added to the projected rate as stated: flat across periods, after seasonality, outside the blend.

Estimating assumptions with actuarialpy

Estimation is explicit and separate from projection execution:

from projectionmodels.integrations.actuarialpy import (
    estimate_completion,
    estimate_credibility,
    estimate_seasonality,
    estimate_trend,
)

completion = estimate_completion(
    "claim_completion",
    payment_history,
    by=["claim_type"],
    origin_col="incurred_month",
    valuation_col="paid_month",
    amount_col="paid_claims",
)

seasonality = estimate_seasonality(
    "claim_seasonality",
    completed_history,
    by=["claim_type"],
    date_col="incurred_month",
    value_col="completed_claims",
    exposure_col="member_months",
)

trend = estimate_trend(
    "claim_trend",
    deseasonalized_history,
    by=["claim_type"],
    date_col="incurred_month",
    value_col="deseasonalized_claims",
    exposure_col="member_months",
)

credibility = estimate_credibility(
    "claim_credibility",
    experience_history,
    method="limited_fluctuation",
    by=["group_id", "claim_type"],
    exposure_col="claim_count",
    full_credibility_standard=2_000,
)

The returned assumptions retain indicated values and diagnostics. An actuary can replace the indication while preserving the audit trail:

selected_trend = trend.select(selected_table, note="2027 pricing selection")

Expenses

ExpenseProjection supports:

• per_exposure
• fixed_monthly
• percent_premium
• percent_claims

Each expense type may have its own trend and projection component.

Date handling

ProjectionDates supports entry, exit, renewal, issue, and experience dates. Records can be inactive before entry or after exit, and exposure can be whole- period or daily-prorated.

DateCohort adds reportable classifications such as existing versus new business:

records = pm.DateCohort(
    "business_origin",
    "effective_date",
    split_date="2027-01-01",
    before_label="existing",
    on_or_after_label="new_business",
).apply(records)

Results

summary = results.summarize(
    by=["scenario", "product_id", "calendar_year"],
    measures=["member_months", "premium", "projected_claims", "claims_per_exposure"],
)

ProjectionResults retains measure grain. It counts exposure once when claim type is removed from a summary and recalculates per-exposure rates and loss ratios from their summed numerators and denominators.

Advanced models

Custom deterministic roll-forwards remain available, but are deliberately moved out of the primary namespace:

import projectionmodels.advanced as pma

model = pma.ProjectionModel(...)

Use this only when the claim, premium, and expense workflows are insufficient. The advanced API remains provisional while the concrete workflows stabilize.

Examples

Primary examples:

examples/health_claims.py
examples/pooled_claims.py
examples/calculated_assumptions.py
examples/renewal_rate_actions.py
examples/date_cohorts.py
examples/expenses.py
examples/underwriting_results.py

Custom-engine examples are under examples/advanced/.

Testing

The test suite imports the installed actuarialpy; it does not replace it with a session-wide fake. CI runs the tests, every example, package builds, and a clean wheel-install smoke test.