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Audit Sample Size Calculator

Audit Sample Size Calculator - Classical Sampling Method

Audit Sample Size Calculator

Classical Sampling Method (Representative Sampling)
This template documents sample size calculation using classical sampling method for OSP (Overall Sampling Procedure) in accordance with International Auditing Standards.

Client & Engagement Information

Population Parameters

Starting serial number of the population
Ending serial number of the population
Calculated as: (Last Voucher - First Voucher) + 1
$

Materiality & Exclusions

$
Tolerable misstatement for this audit area
$
High-value items tested 100% (excluded from sampling)
$
Items excluded for specific reasons (e.g., negative balances)
Account Balance - (Key Items + Other Exclusions)

Assurance Considerations & Factors

Consideration Assessment Impact Factor
IRAM Level
i
Inherent Risk Assessment at the Assertion Level
Higher inherent risk requires more audit evidence. Significant risk = 3.0, Moderate = 2.0, Low = 1.0
3.00
Assurance from Tests of Controls (TOCs)
i
Reliance on Internal Controls
Effectiveness of controls reduces substantive testing. None = 0, Low = 0.5, Moderate = 1.0, Significant = 2.0
0.00
Assurance from Substantive Analytical Procedures (SAPs)
i
Analytical Procedures Evidence
Reliance on analytical procedures reduces detailed testing. None = 0, Low = 0.5, Moderate = 1.0, Significant = 2.0
0.00
Assurance from Other OSPs
i
Other Overall Sampling Procedures
Evidence from related audit procedures. None = 0, Low = 0.5, Moderate = 1.0, Significant = 2.0
0.00
Assurance from Data Analytics (DA)
i
Data Analytics Procedures
Audit evidence obtained through data analytics tools. None = 0, Low = 0.5, Moderate = 1.0, Significant = 2.0
0.00
Total Assurance Factor: 3.00

Sampling Parameters

Accounting populations with high variability require larger samples

Sample Size Calculation Results

Initial Sample Size
-
Based on sampling base and materiality
Variability Adjusted Size
-
After applying variability multiplier
Key Items (100% Tested)
0
High-value items tested separately
Total Sample Items
-
Including key items and sampling items
-
Population Size ÷ Total Sample Items (rounded)
Systematic Selection
Every nth item after random start
Calculation Methodology
Sampling Base = Account Balance - (Key Items + Other Exclusions)
Initial Sample Size = (Sampling Base ÷ Performance Materiality) × Total Assurance Factor
Adjusted Sample Size = Initial Sample Size × Variability Multiplier × Confidence Level
Key Items Count = Based on professional judgment (typically items > materiality threshold)
Total Sample = Adjusted Sample Size + Key Items Count
Sampling Interval = Population Size ÷ Total Sample Items (rounded down)

Sample Selection Details

Parameter Value Description
Population Range - First to last voucher in population
Population Size - Total number of items in population
Sampling Base - Monetary value subject to sampling
Assurance Factor - Combined assurance from all sources
Variability Multiplier - Adjustment for population variability

Notes on Sampling Methodology

International Auditing Standards Compliance: This calculator follows ISA 530 (Audit Sampling) requirements for designing and selecting audit samples. Sample sizes are determined based on risk assessment, materiality, and expected misstatements.
Population Variability Consideration: Accounting populations typically have high variability with few large amounts and many small amounts. When stratification or Monetary Unit Sampling (MUS) is not used, sample size should be increased by 25% (multiplier 1.25) to address this variability.
Tolerable Misstatement: Performance materiality is set at an amount lower than overall materiality to reduce the probability that undetected and uncorrected misstatements exceed materiality. Tolerable misstatement for sampling purposes may be equal to or lower than performance materiality.
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Audit Risk Calculator

ISA Audit Risk Assessment Tool

Professional risk assessment in accordance with International Standards on Auditing

AR = RMM × DR (Conceptual relationship per ISA 200)

Audit Scope & Account Selection

ISA 315 Inherent Risk Assessment

Assess susceptibility to material misstatement before considering controls

ISA 315 Inherent Risk Factors

Inherent risk is the susceptibility of an assertion to material misstatement before considering controls. Assess based on:

  • Complexity: Transactions requiring specialized knowledge
  • Estimation uncertainty: Accounting estimates with high measurement uncertainty
  • Susceptibility to fraud: Assets vulnerable to misappropriation
  • Judgment involved: Areas requiring significant management judgment
  • Recent changes: New accounting requirements or business changes

Professional Judgment Required: Inherent risk assessment requires consideration of both likelihood and potential magnitude of misstatement, not mathematical calculation.

Likelihood of Misstatement Moderate
L
Low
L-M
Low-Mod
M
Moderate
H
High
How likely is a misstatement to occur?
Magnitude Potential Moderate
L
Low
L-M
Low-Mod
M
Moderate
H
High
How material could a misstatement be?
Assessed Inherent Risk (IR)
MODERATE
Moderate Inherent Risk
Based on professional judgment combining likelihood and magnitude assessments

ISA 315 Control Risk Assessment

Evaluate control design and implementation for selected account

ISA 315 Control Risk Assessment

Control risk is the risk that a material misstatement will not be prevented or detected by the entity's internal controls.

Key Principles:

  • Evaluate both design and implementation of controls
  • Ineffective key controls relevant to significant assertions elevate overall control risk
  • Consider both entity-level and transaction-level controls
  • Assess whether controls operate consistently throughout the period

ISA 315 Requirement: When the auditor intends to rely on controls, tests of controls must be performed.

Bank Reconciliation Key Control
Existence Completeness
Monthly reconciliation by independent person with review
Effective
Partially Effective
Ineffective
Payment Authorization Key Control
Accuracy Authorization
Dual authorization for large payments with documented approval
Effective
Partially Effective
Ineffective
Cash Handling Procedures
Existence Security
Segregation of duties for cash handling and physical security
Effective
Partially Effective
Ineffective
Assessed Control Risk (CR)
MODERATE
Moderate Control Risk
Based on evaluation of control design and implementation

ISA Risk Assessment Results

Audit Risk Tolerance
MEDIUM
Professional Judgment
Inherent Risk (IR)
MODERATE
ISA 315 Assessment
Control Risk (CR)
MODERATE
ISA 315 Assessment
Risk of Material Misstatement (RMM)
MODERATE
Combined IR & CR

ISA Risk Assessment Explanation

Step 1: Inherent Risk Assessment (ISA 315)

IR assessed qualitatively based on susceptibility to misstatement considering:

  • Complexity of transactions
  • Estimation uncertainty
  • Susceptibility to fraud
  • Degree of judgment involved

Current assessment: MODERATE based on moderate likelihood and magnitude

Step 2: Control Risk Assessment (ISA 315)

CR assessed based on evaluation of control design and implementation effectiveness:

  • Effectiveness of key controls for significant assertions
  • Consistency of control operation
  • Weakest link principle for key controls

Current assessment: MODERATE based on control evaluation

Step 3: Risk of Material Misstatement (ISA 200)

RMM is a conceptual combination of inherent risk and control risk:

Inherent Risk
+
Control Risk
=
RMM

Current assessment: MODERATE RMM (Moderate IR + Moderate CR)

Step 4: Detection Risk Determination (ISA 200)

Detection Risk is determined by the inverse relationship with RMM:

Higher RMM → Lower acceptable Detection Risk

Lower RMM → Higher acceptable Detection Risk

Based on MODERATE RMM: MODERATE DETECTION RISK is acceptable

ISA 330 Audit Response & Strategy
Recommended Audit Approach (ISA 330)
Based on MODERATE RMM and MODERATE acceptable detection risk, implement a BALANCED AUDIT APPROACH combining control testing and substantive procedures.
Nature of Procedures (ISA 330.6)
Combine tests of controls with substantive procedures. Test operating effectiveness of key controls while performing substantive analytical procedures and tests of details for higher risk assertions.
Timing of Procedures (ISA 330.20)
Consider interim testing of controls with update procedures at period-end. Perform substantive procedures closer to period-end, particularly for higher risk areas.
Extent of Procedures (ISA 330.7)
Apply moderate sample sizes with emphasis on higher risk transactions. Increase extent of testing for areas with identified control deficiencies or higher inherent risk.
Control Reliance Decision
Moderate reliance on controls after testing operating effectiveness. Supplement with substantive procedures for significant assertions.
Key Audit Procedures to Consider
  • Test operating effectiveness of identified key controls
  • Perform substantive analytical procedures on material accounts
  • Execute tests of details for higher risk transactions
  • Consider confirmations for significant balances
  • Test cut-off procedures around period-end
  • Document risk assessment and responses thoroughly
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