Short answer: OÜ invoices need registration number (registrikood), VAT number (if registered), sequential numbering, Estonian address, and proper VAT formatting.
Understanding Estonian OÜ (Osaühing)
OÜ (Osaühing) is the most common company type in Estonia, equivalent to a private limited company. If you're an Estonia e-Resident running a business, you likely have an OÜ.
Key fact: All OÜ companies must follow Estonian invoicing standards, regardless of where the founder lives (digital nomad, e-Resident, etc.).
Mandatory Fields on Every OÜ Invoice
Your OÜ Company Information
- Company Name: Full legal name ending in "OÜ" (e.g., "MyCompany OÜ")
- Registration Number (Registrikood): 8-digit number from e-Business Register (e.g., 12345678)
- Registered Address: Your official Estonian address on file with government
- VAT Number: EE format if VAT-registered (e.g., EE123456789) - required above €40,000 annual revenue
- Contact Information: Business email, phone number, website (recommended)
Invoice Details
- Unique Invoice Number: Must be sequential with no gaps (INV-001, INV-002, INV-003...)
- Invoice Date: Date of issue (DD.MM.YYYY format common in Estonia)
- Payment Terms: Due date or payment period (e.g., Net 14, Net 30)
- Order/Reference Number: Transaction ID for tracking
Customer Information
- Customer Name: Full legal name (company or individual)
- Billing Address: Complete address including country
- VAT Number: Required for B2B EU transactions (triggers reverse charge)
- Registration Number: Helpful for business customers
Financial Breakdown
- Product/Service Description: What was sold
- Quantity: Number of units or licenses
- Unit Price: Price per item in euros (€)
- Net Amount: Subtotal before VAT
- VAT Rate: 22% (standard), 9% (reduced), or 0% (reverse charge/export)
- VAT Amount: Tax amount in euros
- Gross Total: Final amount to be paid
OÜ VAT Registration Requirements
When Must an OÜ Register for VAT?
€40,000 Threshold: You must register for VAT when your taxable turnover exceeds €40,000 in a 12-month period.
Before VAT Registration (Revenue Under €40,000)
- ✅ Include OÜ registration number on invoices
- ✅ Use registered Estonian address
- ✅ Sequential invoice numbering
- ❌ No VAT number required
- ❌ No VAT breakdown on invoices
- ❌ Cannot charge VAT to customers
After VAT Registration (Revenue Above €40,000)
- ✅ Display your EE VAT number on all invoices
- ✅ Show VAT breakdown (net, VAT rate, VAT amount, gross)
- ✅ Apply reverse charge for B2B EU transactions
- ✅ Submit monthly or quarterly VAT returns to Maksu- ja Tolliamet
- ✅ Include "Reverse charge applies" notation when applicable
OÜ Invoice Numbering Rules
Estonian law requires sequential invoice numbering with no gaps.
✅ Correct Sequential Numbering:
INV-2024-001
INV-2024-002
INV-2024-003
INV-2024-004
❌ Incorrect (Gaps Not Allowed):
INV-2024-001
INV-2024-002
INV-2024-005 ← Gap! Not compliant
INV-2024-008
Why it matters: The Estonian Tax Authority (Maksu- ja Tolliamet) uses sequential numbering to verify all transactions are reported. Gaps suggest missing invoices or tax evasion.
OÜ vs AS vs FIE: Invoice Differences
| Company Type | Full Name | Invoice Requirements |
|---|---|---|
| OÜ | Osaühing (Private Limited Company) | 8-digit registration number, VAT if >€40k, sequential numbering |
| AS | Aktsiaselts (Public Limited Company) | Same as OÜ + additional disclosure requirements |
| FIE | Füüsilisest isikust ettevõtja (Sole Proprietor) | Personal ID number, different VAT threshold (€25k) |
Most e-Residents have OÜ because it's the standard company type for digital businesses.
Estonian Reverse Charge for OÜ B2B Transactions
When your OÜ invoices another EU business (B2B), reverse charge rules apply if:
- ✅ Your OÜ has an Estonian VAT number (EE format)
- ✅ Customer has a valid EU VAT number (different country)
- ✅ Service is digital/provided remotely
- ✅ You're selling to a business, not a consumer
Reverse Charge Invoice Format:
- VAT Rate: 0%
- VAT Amount: €0.00
- Display both VAT numbers (yours + customer's)
- Include notation: "Reverse charge applies - EU Directive 2006/112/EC"
Estonian Accounting Software Compatibility
Your OÜ invoices must work with Estonian accounting software:
- Merit Aktiva: Most popular for e-Residents (web-based)
- Directo: Enterprise-level accounting system
- Horizon: Common for small-medium OÜ companies
- Excel/Manual: Simple bookkeeping for small OÜs
Format requirements: Professional PDF with all fields clearly labeled, ready for manual entry or attachment to accounting records.
Common OÜ Invoice Mistakes to Avoid
❌ Invoice Rejected - Common Errors:
- Missing Registration Number: "Where's your registrikood?"
- Gaps in Numbering: "Invoice 005 missing, where is it?"
- Wrong VAT Format: "Your VAT number should start with EE"
- No Reverse Charge Notation: "This B2B EU invoice needs reverse charge"
- Inconsistent Company Name: "Name doesn't match Business Register"
- Missing Estonian Address: "Need your registered Estonian address"
OÜ Invoice Format Example
Invoice #INV-2024-042
From:
MyCompany OÜ
Registration Number: 12345678
VAT Number: EE123456789
Roosikrantsi 11, Tallinn 10119, Estonia
Email: billing@mycompany.com
To:
CustomerCompany GmbH
VAT Number: DE987654321
Munich, Germany
Invoice Date: 15.02.2024
Payment Due: 16.03.2024 (Net 30)
| Product/Service | Qty | Price | Total |
| SaaS Subscription - Pro Plan | 1 | €99.00 | €99.00 |
Net Amount: €99.00
VAT (0% - Reverse Charge): €0.00
Total Due: €99.00
Reverse charge applies - EU Directive 2006/112/EC
How CSV2Invoice Handles OÜ Requirements
Our invoice generator automatically includes all OÜ requirements:
- ✅ Field for 8-digit registration number (registrikood)
- ✅ EE format VAT number field
- ✅ Automatic sequential numbering (no gaps)
- ✅ Estonian address fields
- ✅ Automatic reverse charge for B2B EU transactions
- ✅ Professional PDF format for accountants
- ✅ Compatible with Merit Aktiva, Directo, Horizon