Rule of 70 GDP Doubling Time

Inspectable records

Ledger state

The current ledger marks this instrument verified clean within the source-bound verification corpus.

Area

Finance, Economics & Business (educational only — never individualized investment, tax, or legal advice)

Tranche

tranche-5

Evidence ID

t5-196

Ledger rows

1

No ledger note is attached.

Review findings

The arithmetic formula is standard and the existing honest label of "Rough approximation" is appropriate. Review is required because the specification omits validation behavior for zero and negative rates and does not unambiguously define whether the UI accepts percentage points or decimal fractions.

Formula and scope findings

• The formula years ≈ 70 / growth_rate_percent is the standard Rule of 70 approximation for a positive, constant, compounded annual growth rate. The spec does not state the required positive-rate constraint or behavior for zero and negative rates.
• The input representation is not fully explicit: growth_rate_percent must be entered as percentage points (for example, 7 for 7%), not as a decimal fraction (0.07).

Unit assumptions

• The growth rate is an annual percentage expressed in percentage points, such as 2.5 for 2.5% per year.
• The calculation assumes constant annual compounding.
• GDP growth and the intended GDP measure must use matching units and definitions, such as both real GDP or both nominal GDP.
• The output is an approximate number of years.

Boundary hardening

BREAK_CLAIMED · SELF_FLAGGED

A zero growth rate causes division by zero and must be rejected or returned as undefined. Negative growth produces a raw negative quotient that is not a meaningful doubling time and therefore requires an implicit validity branch. The percent-versus-decimal convention can also produce a materially different result if the input unit is misunderstood.

Errata and corrections

No applied erratum is attached to this unique-name record.

Inspectable example

4 review vectors are recorded. One source-bound sample is shown below.

{
  "inputs": {
    "annual_gdp_growth_rate_percent": 2.5
  },
  "expected_outputs": {
    "years_to_double": 28
  },
  "working": "Apply Rule of 70: years ≈ 70 / growth rate %. Substitute 2.5: 70 / 2.5 = 28. Expected result: 28 years."
}

Related workflows

No source-defined multi-instrument workflow membership is recorded.

Sources and evidence

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

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