# ERP vs Custom System: What Growing Companies Should Know > ERP vs custom software: how to decide which processes belong in a packaged ERP, which need a custom system, and how to compare five-year costs. - URL: https://weaveward.com/blog/erp-vs-custom-system - Published: 2024-04-16 - Updated: 2024-04-16 - Category: Business Systems - Tags: erp, custom software, build vs buy, system integration, business systems - Author: Weaveward Team If you are weighing ERP vs custom software, the honest answer is usually "both, in different places." Buy an ERP for processes that work the same way in most companies, such as accounting, tax, purchasing and basic inventory. Build custom software for the processes that make you different, or that an ERP could only handle with heavy modification. Many growing companies end up with an ERP core and a few custom applications connected to it. The hard part is drawing that line. Draw it too far toward the ERP and your team spends years fighting screens that do not match how you work. Draw it too far toward custom and you end up maintaining your own accounting engine, which is rarely a good use of money. Below are the questions that decide the split, the Indonesian requirements to test before signing, and a short process for comparing options with your own scenarios. ## What you are actually comparing An ERP (enterprise resource planning) system is a packaged product whose modules share one database: finance, purchasing, sales, inventory, and often manufacturing and HR. International products such as SAP Business One, Microsoft Dynamics 365 Business Central, Oracle NetSuite and Odoo are usually implemented through partners. Indonesian products such as Accurate and Jurnal are accounting-first systems that also cover inventory and sales. A custom system is software designed around your process and built by your own developers or a software house. You decide the screens, the rules and the integrations, and with the right contract you own the code. We covered the general trade-offs in our guide to [custom software vs off-the-shelf](/blog/custom-software-vs-off-the-shelf); ERP is the largest and most consequential version of that choice. In practice there are three options, not two: - **ERP with configuration only.** You adapt your process to the product's standard flow - **ERP with customization.** A partner modifies the product, and every modification must be retested at each upgrade - **ERP core plus custom applications.** The ERP keeps the books, and separate applications, connected through APIs, handle the work specific to you How the three options compare: | Factor | Packaged ERP | Custom system | ERP core plus custom apps | |---|---|---|---| | Fit with unique processes | Limited to configuration | Designed around you | Unique parts are custom | | Accounting and tax updates | Handled by the vendor | Your responsibility | Handled by the ERP | | Upfront cost | Licenses plus implementation | Development | Both, with smaller scope each | | Ongoing cost | Subscriptions and partner support | Maintenance team | Both, plus integration upkeep | | Upgrades | Vendor schedule; customizations need retesting | Your schedule | ERP upgrades stay cleaner | | Vendor dependency | High | Low if you own the code | Moderate | | Typical fit | Standard, finance-heavy operations | Distinctive operations with few users | Most growing companies | ## Five questions that decide the split ### 1. Is this process standard or a source of advantage? Posting journals, closing the month and issuing tax invoices work much the same in every company, and a packaged ERP already handles them. Your pricing rules for 300 dealers, your production scheduling across two plants, or the way your sales team takes orders over WhatsApp may be exactly why customers choose you. Those are candidates for custom software. ### 2. How much would the ERP need to change? Ask the ERP partner to run your real scenarios, not their standard demo. If most scenarios work with configuration, that is a strong signal for the ERP. If many need custom code inside the ERP, you are building custom software anyway, only inside someone else's product and upgrade cycle. ### 3. What is the five-year cost, not the year-one price? License fees are the most visible cost and often not the largest. Compare these items over five years: - Licenses or subscriptions, and how prices change as you add users or modules - Implementation, data migration and training - Customizations, plus the cost of retesting them at every upgrade - Hosting, backups and security - Internal staff time for administration and support - For custom software: development, hosting and a yearly maintenance budget for fixes and changes ### 4. Who will own the system after go-live? An ERP needs an internal owner who understands both the business process and the configuration. A custom system needs a development team, in-house or contracted, that can fix bugs and add features for years. If you have neither, solve that first. The questions in our guide on [how to choose a software house](/blog/how-to-choose-a-software-house) apply equally to choosing an ERP implementation partner. ### 5. How quickly do you need it working? A standard ERP module can be running sooner than a custom build of the same scope, provided your process fits it. A custom system can deliver the most important workflow first and grow from there. Either way, speed depends mostly on how quickly your team makes decisions and cleans up its master data. ## The hybrid pattern most growing companies end up with The pattern that suits many mid-sized companies looks like this: the ERP holds the general ledger, tax, purchasing and stock valuation. Custom applications handle work that touches customers, field staff or specialized operations. An integration layer moves data between them. Take a hypothetical distributor with 40 salespeople who visit shops and send orders through WhatsApp. A packaged ERP has a sales order screen, but it is designed for office staff at a desk. A custom mobile ordering app can show each salesperson their customer list, prices and current stock, then create sales orders in the ERP through its API. Finance still sees every transaction in one place, and the sales team gets a tool built for a phone on the road. Other common custom pieces around an ERP: - Dealer or customer portals for ordering, invoices and payment status - Production planning or quality inspection apps on the factory floor - Delivery tracking for drivers, with proof-of-delivery photos - Reconciliation of Tokopedia and Shopee orders, and of payments received via QRIS or virtual accounts Before you commit to this pattern, confirm that the ERP edition you are buying exposes the APIs you need, whether API access costs extra and whether usage is limited. What is available often depends on the edition and on whether the system is cloud-hosted. ## Indonesian requirements to test before you choose Whatever you pick, test these local requirements early. This is where generic products most often fall short. - **e-Faktur and tax reporting.** VAT-registered businesses (PKP) issue tax invoices through e-Faktur, the system run by the Directorate General of Taxes (DJP). Ask whether the system produces the import file e-Faktur expects or integrates through an authorized tax application provider (PJAP), and how quickly it is updated when DJP changes its formats - **Payroll rules.** If HR is in scope, check BPJS Kesehatan and BPJS Ketenagakerjaan contributions and PPh 21 withholding, including the average effective rate (TER) scheme that applies from January 2024 - **Multi-currency.** Importers who buy in US dollars and sell in Rupiah need correct exchange rate handling, including realized and unrealized exchange gains and losses - **Language and devices.** Warehouse and field staff may need Bahasa Indonesia screens and an interface that works well on an Android phone - **Personal data.** Indonesia's Personal Data Protection Law (Law No. 27 of 2022, UU PDP) covers customer and employee data, and its two-year transition period ends in October 2024. Ask where data is hosted, who can access it and how access is logged. Regulated sectors such as banking and insurance may have extra rules on data location - **Local support.** Check that the partner can visit your site and responds within your working hours ## How to decide in weeks instead of months You can run this comparison with your own team: 1. **List your core processes** (order to cash, procure to pay, production, stock, payroll) and mark each one "standard" or "differentiating." Be strict: most processes are standard 2. **Write 8 to 12 real scenarios** with actual examples, such as "partial delivery, remainder back-ordered, one tax invoice per shipment" or "dealer-specific price with a volume discount." 3. **Ask two or three ERP partners to run those scenarios** with your data, and note which ones need customization 4. **Ask a software house to estimate the custom pieces and integrations** for the scenarios the ERP cannot handle cleanly 5. **Build a five-year cost table** for each option using the cost items above, with the assumptions written next to each number 6. **Check data readiness.** Count duplicate customers, inconsistent item codes and missing prices. This drives migration effort more than record counts do Watch for these warning signs along the way: - The plan is to customize the ERP until it looks like your current spreadsheets. If you recognize yourself in [10 signs your business has outgrown spreadsheets](/blog/signs-business-outgrown-spreadsheets), the goal is a better process, not a copy of the old one - Someone proposes building accounting, tax and general ledger logic from scratch. Tax rules change, and every change becomes your maintenance task - Nobody inside the company has the time or authority to own the project - The decision is made from a slide deck before anyone has seen your scenarios running ## FAQ ### Is Odoo an ERP or a custom system? Odoo is an ERP. Its core is a packaged product with standard modules for accounting, sales, inventory and more. It is also open to extensive customization through its module system. The usual rule still applies: configuration is cheap to maintain, while custom modules must be tested, and sometimes rewritten, each time you move to a new version. ### Can we start with accounting software and move to a full ERP later? Yes, and many companies do. Accounting software such as Accurate or Jurnal can carry a business for years. Prepare for the move by keeping master data clean from the start: consistent item codes, one record per customer and a stable chart of accounts. Any custom apps should talk to the accounting system through APIs, so they can be reconnected to an ERP later. ### How long does an ERP implementation take compared with a custom build? As a rough planning range, a small ERP rollout covering finance, purchasing, sales and inventory for one company often takes 3 to 6 months, assuming a committed process owner and reasonably clean data. A focused custom application for one workflow, built by a 3 to 4 person team, often takes 3 to 5 months. Scope, data cleanup and decision speed move these numbers more than the technology does. ### Do we own the source code of a custom system? Only if your contract says so. Make sure the agreement transfers intellectual property or grants you a perpetual license, gives you access to the code repository throughout the project, and includes documentation and deployment scripts. Without these, switching vendors later can be as hard as leaving an ERP. Ask about this before signing, not at handover. ## How Weaveward can build this for you We would start with a short process review: map your order-to-cash and procure-to-pay flows, mark what is standard and what is distinctive, and run your real scenarios against the ERP you use or are considering. The first deliverable is a written split of ERP and custom scope, with a five-year cost table and the integrations each option needs. If custom work is justified, we would build the ERP integration first, then the most painful workflow on top of it, and validate both with a parallel run on real transactions before switching over. See how we approach [custom business systems and ERP integration](/services/business-systems), or [talk to our team](/contact) about the processes you are trying to fit.