Multiple Bid Fair Price Range Calculator

ANA›Life Services Authority›National Calculator Authority›Multiple Bid Fair Price Range Calculator

.calc-container { max-width: 640px; margin: 2rem 0; padding: 1.5rem; background: #fff; border: 1px solid #ddd; border-radius: 8px; box-shadow: 0 1px 3px rgba(0,0,0,0.06); font-family: system-ui, -apple-system, sans-serif; } .calc-container h3 { font-family: Georgia, serif; font-size: 1.15rem; color: #1a1a1a; margin-bottom: 1rem; padding-bottom: 0.5rem; border-bottom: 2px solid var(--ac, #3d5a80); } .calc-row { display: flex; align-items: center; gap: 0.75rem; margin-bottom: 0.75rem; flex-wrap: wrap; } .calc-row label { min-width: 160px; font-size: 0.9rem; color: #333; font-weight: 500; } .calc-row input[type="number"], .calc-row select { flex: 1; min-width: 120px; max-width: 200px; padding: 0.5rem 0.6rem; border: 1px solid #ccc; border-radius: 4px; font-size: 0.9rem; font-family: system-ui, sans-serif; color: #1a1a1a; background: #fafaf8; } .calc-row input:focus, .calc-row select:focus { outline: none; border-color: var(--ac, #3d5a80); box-shadow: 0 0 0 2px rgba(26,74,138,0.12); } .calc-row .unit { font-size: 0.82rem; color: #888; min-width: 30px; } .calc-btn { display: inline-block; margin-top: 0.5rem; padding: 0.55rem 1.5rem; background: var(--ac, #3d5a80); color: #fff; border: none; border-radius: 4px; font-size: 0.9rem; font-weight: 600; cursor: pointer; font-family: system-ui, sans-serif; } .calc-btn:hover { opacity: 0.9; } .calc-result { margin-top: 1.25rem; padding: 1rem 1.25rem; background: #f0f6fc; border-left: 3px solid var(--ac, #3d5a80); border-radius: 0 6px 6px 0; display: none; } .calc-result.visible { display: block; } .calc-result-label { font-size: 0.78rem; text-transform: uppercase; letter-spacing: 0.06em; color: #666; margin-bottom: 0.25rem; } .calc-result-value { font-size: 1.6rem; font-weight: 700; color: var(--ac, #3d5a80); } .calc-result-detail { font-size: 0.85rem; color: #555; margin-top: 0.5rem; line-height: 1.5; } .calc-note { margin-top: 1rem; font-size: 0.8rem; color: #888; font-style: italic; } .calc-grid { display: grid; grid-template-columns: 1fr 1fr; gap: 0.75rem; margin-top: 0.75rem; } .calc-grid-item { padding: 0.6rem 0.8rem; background: #f8f9fa; border-radius: 4px; border: 1px solid #eee; } .calc-grid-item .label { font-size: 0.75rem; color: #888; text-transform: uppercase; letter-spacing: 0.04em; } .calc-grid-item .value { font-size: 1.1rem; font-weight: 600; color: #1a1a1a; } @media (max-width: 720px) { .calc-row { flex-direction: column; align-items: flex-start; gap: 0.3rem; } .calc-row label { min-width: auto; } .calc-row input[type="number"], .calc-row select { max-width: 100%; width: 100%; } .calc-grid { grid-template-columns: 1fr; } } .calc-chart { margin: 1rem 0; text-align: center; } .calc-chart svg { max-width: 100%; height: auto; } .calc-chart-legend { display: flex; flex-wrap: wrap; justify-content: center; gap: 0.6rem 1.2rem; margin-top: 0.6rem; font-size: 0.8rem; color: #555; } .calc-chart-legend span { display: inline-flex; align-items: center; gap: 0.3rem; } .calc-chart-legend i { display: inline-block; width: 10px; height: 10px; border-radius: 2px; font-style: normal; } .calc-related { max-width: 640px; margin: 2rem 0 1rem; padding: 1.25rem 1.5rem; background: #f8f9fa; border: 1px solid #e8e8e8; border-radius: 8px; } .calc-related h3 { font-family: Georgia, serif; font-size: 1rem; color: #1a1a1a; margin: 0 0 0.75rem; padding-bottom: 0.4rem; border-bottom: 2px solid var(--ac, #3d5a80); } .calc-related-list { list-style: none; padding: 0; margin: 0 0 0.75rem; display: grid; grid-template-columns: 1fr 1fr; gap: 0.4rem 1.5rem; } .calc-related-list li a { font-size: 0.88rem; color: var(--ac, #3d5a80); text-decoration: none; } .calc-related-list li a:hover { text-decoration: underline; } .calc-browse-all { margin: 0.5rem 0 0; font-size: 0.9rem; font-weight: 600; } .calc-browse-all a { color: var(--ac, #3d5a80); text-decoration: none; } .calc-browse-all a:hover { text-decoration: underline; } @media (max-width: 720px) { .calc-related-list { grid-template-columns: 1fr; } }

Multiple Bid Fair Price Range Calculator

Enter up to 10 contractor bids to calculate the statistically fair price range, identify outliers, and determine a recommended budget target.

Number of Bids (2–10)

Outlier Sensitivity

Standard (1.5× IQR) Strict (1.0× IQR) Relaxed (2.0× IQR)

Contingency Buffer (%)

Calculate Fair Price Range

(function() { function renderBidInputs() { var n = parseInt(document.getElementById('mul_num_bids').value) || 3; n = Math.min(10, Math.max(2, n)); var container = document.getElementById('mul_bid_inputs'); var existing = container.querySelectorAll('input'); var vals = []; existing.forEach(function(inp) { vals.push(inp.value); }); container.innerHTML = ''; for (var i = 0; i 50) { resultDiv.style.display = 'block'; resultDiv.innerHTML = 'Contingency must be between 0% and 50%.'; return; }

var bids = []; var errors = []; for (var i = 0; i 0) { resultDiv.style.display = 'block'; resultDiv.innerHTML = '' + errors.join('') + ''; return; }

// Sort bids var sorted = bids.slice().sort(function(a, b) { return a - b; });

// Quartiles & IQR var q1 = percentile(sorted, 25); var q2 = percentile(sorted, 50); // median var q3 = percentile(sorted, 75); var iqr = q3 - q1;

// Outlier fences var lowerFence = q1 - sensitivity * iqr; var upperFence = q3 + sensitivity * iqr;

var validBids = []; var outliers = []; bids.forEach(function(b, idx) { if (b upperFence) { outliers.push({ index: idx + 1, value: b }); } else { validBids.push(b); } });

// If all bids are outliers (edge case), use all bids if (validBids.length === 0) validBids = bids.slice();

var validSorted = validBids.slice().sort(function(a, b) { return a - b; }); var avg = mean(validBids); var sd = stddev(validBids, avg); var validMin = validSorted[0]; var validMax = validSorted[validSorted.length - 1];

// Fair price range: mean ± 1 standard deviation (clamped to valid min/max) var fairLow = Math.max(validMin, avg - sd); var fairHigh = Math.min(validMax, avg + sd);

// If SD is 0 (all bids identical), use ±5% of mean if (sd === 0) { fairLow = avg * 0.95; fairHigh = avg * 1.05; }

// Recommended target: weighted midpoint (60% median, 40% mean of valid bids) var validMedian = percentile(validSorted, 50); var recommendedTarget = 0.6 * validMedian + 0.4 * avg;

// Budget with contingency var budgetWithContingency = recommendedTarget * (1 + contingency / 100);

// Spread analysis

var overallSpread = ((sorted[sorted.length - 1] - sorted[0]) / sorted[0]) * 100;

var validSpread = validBids.length > 1

? ((validMax - validMin) / validMin) * 100

0;

// Coefficient of variation var cv = avg > 0 ? (sd / avg) * 100 : 0;

// Bid ranking var ranked = bids.map(function(b, i) { return { index: i + 1, value: b }; }).sort(function(a, b) { return a.value - b.value; });

// Build output var outlierHtml = ''; if (outliers.length > 0) { var oList = outliers.map(function(o) { var dir = o.value > upperFence ? 'HIGH' : 'LOW'; return '- Bid ' + o.index + ': ' + fmt(o.value) + ' [OUTLIER – ' + dir + ']'; }).join(''); outlierHtml = '' + '⚠ Outlier Bids Detected (excluded from fair range):' + oList + ''; }

var rankRows = ranked.map(function(r, pos) {

var isOutlier = outliers.some(function(o) { return o.index === r.index; });

var inRange = r.value >= fairLow && r.value ⚠ Outlier'

(inRange ? ' ✓ In Range' : ''); return '' + (pos + 1) + 'Bid ' + r.index + '' + '' + fmt(r.value) + badge + '' + '' + (avg > 0 ? ((r.value - avg) / avg * 100).toFixed(1) + '%' : '—') + ''; }).join('');

var spreadLabel = overallSpread ' + '' + 'RankBidAmountvs. Mean' + '' + rankRows + '' +

'' +

'' + 'Statistical Summary' + 'All Bids Mean: ' + fmt(mean(bids)) + '' + 'Valid Bids Mean: ' + fmt(avg) + '' + 'Median (valid): ' + fmt(validMedian) + '' + 'Std Deviation: ' + fmt(sd) + '' + 'Coeff. of Variation: ' + cv.toFixed(1) + '%' + '' +

'' + 'Quartile Analysis' + 'Q1 (25th pct): ' + fmt(q1) + '' + 'Q2 / Median: ' + fmt(q2) + '' + 'Q3 (75th pct): ' + fmt(q3) + '' + 'IQR: ' + fmt(iqr) + '' + 'Outlier Fences: ' + fmt(Math.max(0, lowerFence)) + ' – ' + fmt(upperFence) + '' +

'' + 'Spread Analysis' + 'Overall Spread: ' + overallSpread.toFixed(1) + '%' + 'Valid Bid Spread: ' + validSpread.toFixed(1) + '%' + 'Assessment: ' + spreadLabel + '' + 'Valid Bid Range: ' + fmt(validMin) + ' – ' + fmt(validMax) + '' +

'' + 'Outlier Detection' + 'Sensitivity: ' + sensitivity + '× IQR' + 'Total Bids: ' + bids.length + '' + 'Valid Bids: ' + validBids.length + '' + 'Outliers Found: ' + outliers.length + '' +

'' +

'' + '### ✅ Fair Price Range: ' + fmt(fairLow) + ' – ' + fmt(fairHigh) + ' ' + 'Recommended Target: ' + fmt(recommendedTarget) + '' + 'Budget with ' + contingency + '% Contingency: ' + fmt(budgetWithContingency) + '' + ''; };

// Initialize on load renderBidInputs(); })();

#### Formulas Used

Quartiles: Q1 = 25th percentile, Q2 = 50th percentile (median), Q3 = 75th percentile using linear interpolation.

Interquartile Range (IQR): IQR = Q3 − Q1

Outlier Fences: Lower = Q1 − (k × IQR), Upper = Q3 + (k × IQR), where k = sensitivity multiplier (default 1.5).

Valid Bids Mean (μ): μ = Σ(valid bids) / n

Standard Deviation (σ): σ = √[ Σ(xᵢ − μ)² / n ]

Fair Price Range: [max(validMin, μ − σ), min(validMax, μ + σ)]

Recommended Target: 0.6 × median + 0.4 × mean (of valid bids)

Budget with Contingency: Target × (1 + contingency% / 100)

Coefficient of Variation: CV = (σ / μ) × 100%

Spread: ((max − min) / min) × 100%

#### Assumptions & References

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References

• ANA
• Life Services Authority