scmgo

scmgo is a Go library for practical inventory and supply-chain calculations.

The inventory package provides clear and reusable functions for common inventory policy calculations such as reorder point, safety stock, EOQ, min/max levels, lead-time demand helpers, service-level-based threshold planning, and policy summary helpers.

The goal is to keep the API:

• simple
• transparent
• practical
• easy to embed in Go applications

Stability

The inventory package is released as v1.0.0 and is intended to provide a stable public API for practical inventory policy calculations.

Current Scope

As of v1.0.0, the inventory package includes:

• ReorderPoint
• SafetyStockBasic
• EOQ
• MinMaxLevels
• ZScoreForServiceLevel
• SafetyStockWithServiceLevel
• ReorderPointWithServiceLevel
• DemandDuringLeadTime
• StdDevDemandDuringLeadTime
• TargetInventoryLevel
• TargetInventoryLevelWithServiceLevel
• MinMaxLevelsWithServiceLevel
• BuildPolicySummary
• BuildPolicySummaryWithServiceLevel

Why scmgo

Many inventory and supply-chain calculations still live in spreadsheets, internal notes, or one-off scripts. scmgo provides a lightweight Go-native alternative for developers building:

• inventory tools
• supply-chain applications
• planning dashboards
• internal operations services
• educational and analytical tools

The package is intentionally small, explicit, and easy to embed.

Installation

go get github.com/motah-fard/scmgo/inventory@latest

Package

Current package:

• github.com/motah-fard/scmgo/inventory

Quick Start

package main

import (
	"fmt"
	"log"

	"github.com/motah-fard/scmgo/inventory"
)

func main() {
	summary, err := inventory.BuildPolicySummary(inventory.PolicySummaryInput{
		DailyDemand:      100,
		LeadTimeDays:     5,
		ReviewPeriodDays: 7,
		SafetyStockUnits: 50,
	})
	if err != nil {
		log.Fatal(err)
	}

	fmt.Printf("reorder point: %.0f\n", summary.ReorderPoint)
	fmt.Printf("target level: %.0f\n", summary.TargetInventoryLevel)
}

Policy Summary Helpers

These helpers provide a higher-level API for common inventory planning workflows. They are useful when you want one call to return the main planning outputs instead of assembling them manually from several lower-level functions.

Deterministic Policy Summary

Builds a policy summary from average demand, lead time, review period, and fixed safety stock.

summary, err := inventory.BuildPolicySummary(inventory.PolicySummaryInput{
	DailyDemand:      100,
	LeadTimeDays:     5,
	ReviewPeriodDays: 7,
	SafetyStockUnits: 50,
})

Returned fields include:

• expected demand during lead time
• safety stock
• reorder point
• target inventory level
• min level
• max level

Service-Level Policy Summary

Builds a policy summary using service-level-based reorder point logic and demand variability.

summary, err := inventory.BuildPolicySummaryWithServiceLevel(inventory.PolicySummaryServiceLevelInput{
	DailyDemand:        100,
	LeadTimeDays:       5,
	ReviewPeriodDays:   7,
	DemandStdDevPerDay: 20,
	ServiceLevel:       0.95,
})

This is useful for dashboards, reorder recommendations, and embedded inventory planning logic where service-level assumptions matter.

Available Functions

Reorder Point

Calculates reorder point using average daily demand, lead time, and safety stock.

rp, err := inventory.ReorderPoint(inventory.ReorderPointInput{
	AvgDailyDemand:   100,
	LeadTimeDays:     5,
	SafetyStockUnits: 50,
})

Basic Safety Stock

Calculates safety stock using a max-demand and average-demand approach.

ss, err := inventory.SafetyStockBasic(inventory.SafetyStockInput{
	MaxDailyDemand:  120,
	MaxLeadTimeDays: 7,
	AvgDailyDemand:  100,
	AvgLeadTimeDays: 5,
})

EOQ

Calculates economic order quantity.

eoq, err := inventory.EOQ(inventory.EOQInput{
	AnnualDemand:       10000,
	OrderingCost:       50,
	HoldingCostPerUnit: 2,
})

Min/Max Levels

Calculates minimum and maximum inventory levels from reorder point and order quantity.

levels, err := inventory.MinMaxLevels(inventory.MinMaxInput{
	ReorderPoint:  300,
	OrderQuantity: 200,
})

Z-Score for Service Level

Converts a target cycle service level into a standard normal z-score.

z, err := inventory.ZScoreForServiceLevel(0.95)

Safety Stock with Service Level

Calculates safety stock using demand variability, lead time, and a target service level.

ss, err := inventory.SafetyStockWithServiceLevel(inventory.SafetyStockWithServiceLevelInput{
	StdDevDailyDemand: 10,
	LeadTimeDays:      4,
	ServiceLevel:      0.95,
})

Reorder Point with Service Level

Calculates reorder point using average demand, lead time, demand variability, and a target service level.

rp, err := inventory.ReorderPointWithServiceLevel(inventory.ReorderPointWithServiceLevelInput{
	AvgDailyDemand:    50,
	LeadTimeDays:      4,
	StdDevDailyDemand: 10,
	ServiceLevel:      0.95,
})

Demand During Lead Time

Calculates expected demand during lead time.

d, err := inventory.DemandDuringLeadTime(inventory.DemandDuringLeadTimeInput{
	AvgDailyDemand: 100,
	LeadTimeDays:   5,
})

Standard Deviation of Demand During Lead Time

Calculates the standard deviation of demand during lead time.

sd, err := inventory.StdDevDemandDuringLeadTime(inventory.StdDevDemandDuringLeadTimeInput{
	StdDevDailyDemand: 10,
	LeadTimeDays:      4,
})

Target Inventory Level

Calculates target inventory level from expected demand coverage and safety stock.

level, err := inventory.TargetInventoryLevel(inventory.TargetInventoryLevelInput{
	ExpectedDemandDuringLeadTime: 500,
	SafetyStockUnits:             50,
})

Target Inventory Level with Service Level

Calculates target inventory level using average demand, lead time, demand variability, and a target service level.

level, err := inventory.TargetInventoryLevelWithServiceLevel(inventory.TargetInventoryLevelWithServiceLevelInput{
	AvgDailyDemand:    50,
	LeadTimeDays:      4,
	StdDevDailyDemand: 10,
	ServiceLevel:      0.95,
})

Min/Max Levels with Service Level

Calculates min/max inventory levels using a service-level-based reorder point and a fixed order quantity.

levels, err := inventory.MinMaxLevelsWithServiceLevel(inventory.MinMaxLevelsWithServiceLevelInput{
	AvgDailyDemand:    50,
	LeadTimeDays:      4,
	StdDevDailyDemand: 10,
	ServiceLevel:      0.95,
	OrderQuantity:     200,
})

Design Principles

scmgo is intentionally designed to be:

• small and focused
• explicit rather than clever
• easy to test
• easy to read
• suitable for both production use and teaching

Error Handling

The package validates inputs and returns explicit errors for invalid values such as:

• negative demand
• negative expected demand
• negative lead time
• negative review period
• negative safety stock
• invalid service level
• negative standard deviation
• invalid holding cost

This keeps behavior predictable and makes the library easier to integrate into larger systems.

Assumptions

• Input units must be consistent
• If demand is measured per day, lead time should also be in days
• EOQ uses the classic Wilson EOQ formula
• Service-level calculations assume a normal approximation
• SafetyStockBasic uses a simple max/average demand and lead-time formula
• StdDevDemandDuringLeadTime assumes independent daily demand variability across lead-time periods
• Policy summary helpers combine lead-time coverage, review-period coverage, safety stock, reorder point, target inventory level, and min/max outputs into a single result

Versioning

This project follows semantic versioning.

• v0.1.x focused on core deterministic inventory formulas
• v0.2.x added service-level-based inventory calculations
• v0.3.x added lead-time demand and variability helpers
• v0.4.0 added target inventory level and service-level policy helpers
• v0.5.0 added policy summary helpers and improved API consistency for inventory planning workflows
• v0.6.0 focused on documentation tightening, package consistency, and API stabilization ahead of v1.0.0
• v1.0.0 is the first stable release of the inventory package

Documentation

• Go package docs: pkg.go.dev/github.com/motah-fard/scmgo/inventory
• Releases: github.com/motah-fard/scmgo/releases

License

This project is licensed under the MIT License. See the LICENSE file for details.