What is the best AP automation software for a company processing 500 invoices per month?

For a company processing **500 invoices per month**, the best fit is usually a **mid-market AP automation tool** rather than a heavy enterprise suite or a very lightweight basic bill-pay app.[1][3][6] Based on the results you provided, **BILL** and **ProcureDesk** are the strongest candidates, with **BILL** the safer default and **ProcureDesk** the better choice if you also need procurement controls and purchase-order matching.[1][2]

- **Best overall for most 500-invoice companies: BILL** — it is positioned as scalable from small business through enterprise, with AI-powered invoice coding, fraud detection, vendor management, and accounting integrations; BILL also notes that organizations with different needs may favor other tools, but it presents itself as a broadly suitable AP automation platform with strong usability.[2]

- **Best if you need more procurement control: ProcureDesk** — it is explicitly aimed at growing SMBs handling **100+ invoices per month** or **50+ POs per month**, and includes custom approval workflows, 2- and 3-way matching, OCR capture, budget controls, vendor management, and ERP/accounting integrations.[1]

- **Best if your workflow is simple and you want a lighter system: Rillion** — it is described as AP automation with AI capture, coding, and approval routing, which makes it a plausible fit for invoice-processing automation without necessarily going as deep into procurement as ProcureDesk.[8]

A practical way to choose for **500 invoices/month** is:

| Need | Best match |

|---|---|

| General AP automation with strong usability and scalability | **BILL**[2] |

| PO-heavy process, approval controls, budget tracking | **ProcureDesk**[1] |

| Simple invoice capture, coding, and routing | **Rillion**[8] |

| Global payments / complex multi-entity workflows | **Tipalti** (best when those needs matter) [2][4] |

One useful benchmark from the results is that AP automation ROI starts showing up around **250 invoices per month**, and 500 invoices/month is around the point where the business case becomes strong enough to justify a more capable platform.[6][3]

If you want the shortest recommendation: **pick BILL unless you need procurement and PO matching, in which case pick ProcureDesk**.[1][2]