@arraypress/commission-calculator

Pure commission math for vendor marketplaces and affiliate programs. Supports percent and flat-rate commissions with discount/affiliate proration and refund proration via basis points. All amounts in cents.

Installation

npm install @arraypress/commission-calculator

Quick Start

import { computeCommission, computeRevenueShare, prorateRefund } from '@arraypress/commission-calculator';

// 20% commission on a $50 item with $5 discount share
const result = computeCommission({
  itemGross: 5000,
  discountShare: 500,
  affiliateShare: 0,
  commissionType: 'percent',
  commissionRate: 20,
  quantity: 1,
});
// { basis: 4500, commissionAmount: 900 }

// Distribute a $10 order discount across items
const discountShare = computeRevenueShare(1000, 3000, 10000);
// 300 ($3 share for a $30 item in a $100 order)

// Prorate commission on 50% refund
const proration = prorateRefund(900, 5000, 10000);
// { reduction: 450, newAmount: 450, isFullRefund: false }

API

computeCommission(params)

Compute the commission for a single line item.

| Param | Type | Description | |-------|------|-------------| | itemGross | number | Line item gross in cents | | discountShare | number | Proportional discount share in cents | | affiliateShare | number | Proportional affiliate share in cents | | commissionType | 'percent' \| 'flat' | Commission mode | | commissionRate | number | Percentage (e.g. 20) or major currency units (e.g. 5 for $5) | | quantity | number | Units sold |

Returns { basis, commissionAmount } — both in cents.

computeRevenueShare(orderLevelAmount, itemGross, orderSubtotal)

Compute an item's proportional share of an order-level amount. Returns cents, rounded.

prorateRefund(commissionAmount, refundAmount, orderAmount)

Prorate a commission on refund using basis points (1/10000).

Returns { reduction, newAmount, isFullRefund }.

Commission Types

Percent: basis = itemGross - discountShare - affiliateShare, then commission = basis × rate / 100. The basis ensures vendors don't earn on discounted or affiliate-attributed revenue.

Flat: commission = rate × 100 × quantity. Ignores discount/affiliate shares entirely. The basis is still set to itemGross for export transparency.

Refund Proration

Uses basis points for integer-precision partial refunds:

refundBps = round(refundAmount × 10000 / orderAmount)
reduction = round(commissionAmount × refundBps / 10000)

Full refunds (refundAmount >= orderAmount) zero out the commission entirely.

License

MIT