GDP Growth Rate Calculator mechanism

Model scope

The formulas are conditionally standard, but the specification needs explicit frequency handling, percentage-scaling behavior, multi-period semantics, positive-denominator validation, unit normalization, and a precise definition of how the real-versus-nominal flag affects inputs and labels. The honest label should state whether results are nominal or real and should identify the periods and units supplied by the user.

• The period-over-period formula is standard as a fractional rate, but percentage outputs require multiplying the result by 100 or explicitly formatting the fraction as a percent.
• The annualized formula is correct only for consecutive quarterly observations: (GDP_t/GDP_t-1)^4 - 1. The specification does not define behavior for monthly, annual, irregular, or non-consecutive periods.
• The phrase 'GDP values for two+ periods' does not specify whether multiple periods produce separate adjacent-period rates, a cumulative growth rate, or a compound annual growth rate.
• The real-vs-nominal flag is underspecified: the formula compares whichever GDP series is entered, but does not convert nominal GDP to real GDP or apply a GDP deflator.
• GDP levels must be on a consistent basis, including currency, scale, price basis, and seasonal-adjustment basis, before applying the formula.

Units and conventions

• GDP_t and GDP_t-1 are measured in the same currency, scale, price basis, and seasonal-adjustment basis; the units cancel in the ratio.
• For annualized growth, the two observations are consecutive quarters, so four compounding periods occur per year.
• The displayed percentage equals the fractional formula result multiplied by 100.
• A real GDP calculation requires real GDP inputs, typically at a stated reference-year price basis; the calculator does not itself perform inflation adjustment.
• GDP_t-1 is strictly greater than zero for both formulas to be defined.

Inspectable vector

One of 4 source-bound review vectors:

{
  "inputs": {
    "GDP_t": 20200,
    "GDP_t_minus_1": 20000,
    "units": "billions of currency units",
    "frequency": "quarterly",
    "basis": "real GDP",
    "periods": "consecutive quarters"
  },
  "expected_outputs": {
    "growth_pct": 1,
    "annualized_growth_pct": 4.060401
  },
  "working": "growth = (20,200 - 20,000) / 20,000 = 200 / 20,000 = 0.01; 0.01 × 100 = 1%. annualized = ((20,200 / 20,000)^4 - 1) × 100 = (1.01^4 - 1) × 100 = (1.04060401 - 1) × 100 = 4.060401%."
}

Failure boundary

BREAK_CLAIMED · SELF_FLAGGED

The calculator specification has an undefined-result failure when the prior GDP is zero and does not state a required validation response. It also leaves the annualization branch and sign-reporting conventions insufficiently explicit, creating risks of incorrect results or interpretation.

Other records

Sources and evidence

These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.

• VERIFIED_LEDGER.json
• evidence-tranche5/tranche5-results.json
• BOUNDARY_HAZARD_CATALOG.json