Most Shopify apparel founders are making six-figure buying decisions based on how last season felt, what a sales rep recommended, or how much cash was in the account at market time. That works until it stops working. And when it stops working, it is expensive.
This guide covers the full inventory planning process — from using your Shopify data correctly, to building a buying plan, to managing the season in real time.
Why Inventory Planning Is Different for Apparel Brands
Apparel brands also carry the complexity of size runs. A style might show 60% sell-through at the style level while hiding the fact that every size 8 is gone and the remaining 40% is distributed across sizes that rarely sell. Shopify gives you the data to see this. Most founders do not look at it in the right way — or not at all until there is a problem.
The Four Pillars of Inventory Planning for Shopify Brands
- Demand forecasting. Using historical sales data to project what you will sell in a future period. For small brands, this means taking last year's actuals by month, adjusting for known factors, and arriving at a monthly sales plan to buy against.
- Open-to-buy management. The budgeting layer that controls how much you can spend on inventory for a given period, given your planned sales, current inventory, and already-committed purchases.
- In-season management. Monitoring actual sales versus plan throughout the season and making adjustments — chasing reorders on winners, marking down slow styles before they become dead stock, and rebalancing the OTB as the picture changes.
- End-of-season analysis. Reviewing what actually happened versus what you planned — which styles outperformed, which underperformed, what the size distribution looked like, and what you would do differently.
Most small brands skip pillars 3 and 4 entirely. The brands that build cash and margin are the ones that manage all four.
How to Build a Demand Forecast Using Shopify Data
- Pull last year's weekly sales by month from Analytics → Reports → Sales. Export as CSV. This is your baseline.
- Adjust for what is different this year. New channel, big marketing push, category you are exiting. Normalize one-time events.
- Distribute the annual forecast by month using last year's distribution as the starting point, adjusted for what you know.
- Build the plan at category level, not just total. Tops, bottoms, outerwear, accessories all have different velocity patterns and lead times.
Sell-Through Rate: The Most Important Metric for Apparel Brands
Sell-through tells you whether your initial buy was right-sized. A style at 90% sell-through 6 weeks before season end signals a reorder. A style at 40% with 4 weeks left signals a markdown. A style at 25% mid-season signals an investigation — is it a placement issue, a sizing issue, or did you overbuy?
Size Curve Planning: Where Most Brands Lose Money
Pull your sell-through by size for each major style category over the last two seasons. Which sizes sell out first? Which are consistently left behind? Are you buying 20% of your buy in a size that represents 8% of your sales? That is where your dead stock is living.
The Six Metrics Every Shopify Apparel Brand Should Track
- Sell-through rate by style and category
- Weeks of supply for every active SKU
- Inventory turnover — how many times you sell through average inventory annually
- OTB versus actual spend — are you buying within your plan?
- Markdown rate — what percentage of revenue goes through a sale price?
- Dead stock as a percentage of total inventory value
You do not need a dashboard to track these. A monthly spreadsheet with these six numbers tells you most of what you need to know.
Not sure if you have an inventory problem?
Answer 5 questions and get a plain-English estimate of what better planning could be worth for your brand — no Shopify data required. Calculate My ImpactInventory Planning Software vs. Spreadsheet vs. Consultant
Spreadsheet: Free, flexible, viable up to ~200 active SKUs. Requires discipline to maintain and does not connect directly to Shopify — you export and update manually.
Inventory planning software: Tools like Inventory Planner, Fabrikatör, or Prediko connect directly to Shopify and automate reorder recommendations. Worth evaluating above $1M when manual updating becomes painful.
Fractional planning support: A human planner who builds and manages the system — not software. Worth it when buying decisions are large enough that getting them wrong costs more than the engagement. Typically makes sense at $3M+ or when a founder's time is better spent elsewhere.
Frequently Asked Questions
What Shopify reports are most useful for inventory planning?
The most useful reports are: Sales by product variant (for sell-through analysis), Inventory summary (for current on-hand), and Sales over time (for trend and seasonality). Export these as CSVs monthly and you have the raw data for most planning decisions.
How do I know if I have too much inventory?
Calculate your weeks of supply: on-hand units divided by average weekly sales. If your WOS is significantly higher than 16–20 weeks for most categories, you likely have more inventory than you need at current selling rates.
Do I need inventory planning software to manage my Shopify store?
Not at first. A well-maintained spreadsheet with your key metrics gives you most of what you need up to about $1M–$2M in revenue. Software becomes worth evaluating when manual updating takes more time than it saves or when SKU count makes spreadsheet management unwieldy.
How far ahead should I plan inventory for an apparel brand?
Most apparel brands plan 6–12 months ahead for buying decisions, given lead times of 3–6 months for most vendors. Your seasonal plan should be set 6 months before the season starts, with monthly reviews to adjust as actual sales data comes in.