SimpleSum was born precisely to solve this problem: to be simple and intuitive for freelancers and small businesses, without giving up advanced features such as ATCUD, SAF-T, RSA digital signatures, customer portal, contract management, multi-currency and financial reports seriously.
We will show, in detail, how SimpleSum manages to maintain a light and natural user experience, while hiding a robust fiscal and operational engine under the hood.
What is SimpleSum and for whom is it?
SimpleSum is a Portuguese SaaS invoicing software, designed for:
Freelancers and independent workers who want to invoice simply and quickly compliance.
Micro and small businesses that need more than “just invoices”.
Growing businesses that value reporting, multi-document, multi-currency and integrations.
It is a solution 100% online, with a focus on AT compliance and a user experience that anyone can master in a few minutes, even without background technical.
Because “simple and intuitive” does not mean “limited”
When we say that SimpleSum is “simple and intuitive”, we are not saying that it is “basic”. The simplicity here comes from experience, not capabilities.
Interface designed for everyday life
In everyday life, what the user sees are:
Clear listings with search, filters, and quick actions.
Short, focused forms with helpful (non-intrusive) validations.
Obvious buttons: create, issue, send, download, duplicate.
Messages in plain Portuguese, without unnecessary “technical jargon”.
Behind, however, each click triggers well-defined business rules: plan limits, tax checks, series, digital signatures, auditing, stock control and more more.
Invoicing in compliance with the Tax Authority
One of the pillars of SimpleSum is AT compliance. The aim is that the user does not have to worry about technical details: the software takes care of this automatically.
ATCUD and serial numbering without headaches
Each relevant tax document (invoices, receipt invoices, credit notes, etc.) follows rules of sequential numbering by series. SimpleSum:
Generates the correct numbering according to the type of document and the configured series.
Ensures that there are no sequence breaks that could raise questions in inspections.
Calculates and applies the ATCUD (Unique Document Code) automatically.
For the user, this translates into something simple: choose the series (or accept the default series) and issue the invoice. The rest is handled transparently underneath.
Built-in RSA and QR Code AT digital signatures
To meet the latest AT requirements, SimpleSum:
Generates signatures RSA digital for issued documents, ensuring integrity.
Produces the hash of the document, used by the tax authorities for later validation.
Includes a QR Code on each invoice AT‑compliant, with the fields required by law.
This means that any attempt to change an issued invoice is detectable, and that the documents produced are aligned with current standards – without the user having to “study” the legislation tax.
SAF‑T (PT) export prepared for the accountant
When the time comes to deliver the file to the AT or the accountant, the SimpleSum:
Generates valid SAF‑T (PT) files, based on the documents issued.
Allows you to choose appropriate date ranges (by month, quarter, year, etc.).
Offers a preview mode with statistics (number of customers, number of invoices, total billed).
The result is a less stressful compliance process, with fewer round trips between company and accounting.
Complete document ecosystem: much more than invoiceas
Modern invoicing software cannot be limited to “invoice and receipt”. SimpleSum supports a wide set of documents, aligned with the reality of Portuguese companies:
Documents of sale
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Receipt Invoices
Invoices simplified
Proforma invoices
Consignment invoices
Notes credit
Debit Notes
Receipts
Budgets and proposals
Invoices
Logistics and service documents
Transport guides
Transport guides shipping
Job sheets
Purchase notes / purchase orders
Covenants and recurring contracts
Fixed value, hourly, unit or prepaid agreements.
Automatic or semi-automatic.
Associated documents: reports, annexes and evidence linked to the contract.
Despite this variety, the experience remains consistent: each module has the same usability bases — clear tables, useful filters, familiar forms — so that the The user does not have to relearn the application each time.
Operational management: customers, suppliers, products, stocks and warehouses
Invoicing is just one part of running a business. SimpleSum includes modules that help organize the operation:
Centralized customers and suppliers
Complete record of customers and suppliers, with NIF, contacts and tax data.
History of documents associated with each entity.
Quick search to speed up document creation.
Products, services and categories
Catalog of products and services with configurable prices, VAT rates and exemptions.
Categories for better organization and analysis.
Mass import of products (e.g. from CSV/Excel files, depending on the plan).
Stocks and warehouses
Stock management by warehouse.
Inbound and outbound movements linked to documents (such as guides and invoices).
Clear view of availability, useful for businesses with physical inventory.
Here, once again, the focus is not to sacrifice simplicity: those who need finer control have the tools; Those who don't need it can continue to use the software “as if it were just billing”.
Avenues and Customer Portal: transparency and continuous relationship
Many service businesses work with advisory contracts: monthly hours included, service grants, maintenance recurring, etc. SimpleSum treats this scenario like a first-class citizen.
Flexible retainer contracts
Configuration of retainers for fixed value, hours, units or prepaid.
Definition of start and end dates, billing frequency and limits included.
Recording of actual use (hours/services) and scheduling surpluses.
Customer Portal dedicated to the contract
One of the most advanced features is the Customer Portal for contracts. With a secure link, the customer can:
View the contract summary (reference, name, type, status, value and frequency).
Track usage for the current period (hours/units used vs included, surplus, prepaid balance consumed) contacts of the responsible team (email, telephone, function).
For the service provider, this means fewer repetitive emails (“how many hours have we spent?”, “what is the status of the contract?”) and a more transparent relationship with the client end.
Dashboard and reports: see the business in real time
Right at the entrance, SimpleSum presents a customizable dashboard that answers the question: “How is the business doing in this moment?”.
Dashboard with draggable widgets
Configurable widgets for invoices, customers, products, revenue and reports.
Drag & drop to rearrange the layout to suit each individual's taste user.
Preferences saved per user, respecting the context of each profile.
Advanced financial reports
In addition to the dashboard, there are specific reports for deeper analysis:
Financial overview by period: gross income, credit notes, net income, received, open and overdue.
VAT summary: amounts by VAT rate and by exemption code.
Document listing with advanced filters and export to Excel.
Analysis of exchange rate gains and losses for companies that invoice in multiples currencies.
These reports help transform billing data into useful information for decisions: who are the best customers, in which periods there is more billing, what amounts are yet to be received, how much is gained or lost with exchange rates, and much more.
SaaS plans and subscriptions designed for grow with you
SimpleSum is a subscription SaaS invoicing software, with plans designed for different stages of maturity:
Starter: ideal for freelancers and small businesses that are get started.
Expert: for professionals and online stores that need integrations and more volume.
Business: for multi-company, multi-currency teams and advanced needs.
Instead of just being a price difference, each plan has:
Clear limits: number of documents, users, companies, currencies, etc.
Unlocked features: integrations, multi-currency, stocks, API, among others.
Intelligent control: the system monitors usage and avoids surprises unpleasant.
In practice, the user always knows what they are paying for and what is included, with simple upgrade paths when the business grows.
Security, privacy and internationalization
Because we are talking about billing, customers and payments, security is not optional:
Secure authentication with tokens, email verification and basis for 2FA.
Abuse protection, including attempt logging failed login logs and IP rules.
Audit log of sensitive operations to ensure traceability.
On the experience side, SimpleSum is prepared for:
Be used in Portuguese (PT) and English (EN), with a modular translation system.
Keep the interface cohesive and clear in both languages.
Facilitate collaboration in teams with users who prefer different languages.
Simplicity in form, depth in content
SimpleSum is positioned as simple and intuitive invoicing software for the end user, but its functional basis is anything but simplistic:
Complies with the requirements of the Tax Authority (ATCUD, SAF-T, digital signatures, QR Code, audit log) products, stocks and warehouses.
Offers dashboard and reports that help you make better decisions.
Is based on a SaaS subscription model with scalable plans and modern integrations.
In short, SimpleSum was designed so that you can issue your first invoice in minutes, but still have room to grow without changing software. If you are looking for online invoicing software for Portugal that combines simplicity of use with functional depth, SimpleSum was designed exactly for you.