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The Crypto Support

Posted on Originally published at thecrypto.support AI-assisted

Versioning Tax Rules in a Romanian Crypto App

#backend #validation #cryptocurrency #programming

How to design year-specific Romanian crypto tax rules without scattering rates, thresholds and deadlines throughout your codebase.

Tax rules change.

Code usually lives much longer.

That creates an interesting engineering problem when building financial software:

How do you support changing tax rules without filling the codebase with hardcoded conditions?

At The Crypto Support, we are building crypto tax tooling specifically for users in Romania.

Romanian crypto reporting is a good example of why tax logic should be treated as versioned business rules, not as constants scattered throughout an application.

The dangerous approach

Imagine starting with something simple:

const TAX_RATE = 0.16;
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That works until you need to calculate a previous tax year.

Then someone adds:

if (year === 2025) {
  return profit * 0.10;
}

return profit * 0.16;
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Still manageable.

But tax systems rarely stop at one percentage.

Soon the application also needs to understand:

  • tax years
  • income thresholds
  • reporting deadlines
  • contribution thresholds
  • exemptions
  • transaction categories
  • special cases
  • rule changes introduced by new legislation

At that point, business logic starts leaking everywhere.

Treat rules as data

A cleaner approach is to represent tax rules explicitly.

For example:

const taxRules = {
  2025: {
    incomeTaxRate: 0.10,
    filingYear: 2026
  },

  2026: {
    incomeTaxRate: 0.16,
    filingYear: 2027
  }
};
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Now the calculation engine does not decide which percentage "looks current."

It receives the tax year and loads the rules for that year.

Conceptually:

Transaction history
        ↓
Determine tax year
        ↓
Load rule set
        ↓
Apply calculations
        ↓
Generate report
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This becomes much more useful when rules grow beyond a single rate.

Version the whole rule set

Instead of storing only one tax percentage, the configuration can describe everything relevant to that reporting period.

A simplified structure might look like:

{
  "year": 2026,
  "incomeTaxRate": 0.16,
  "currency": "RON",
  "filingDeadline": "2027-05-25",
  "rulesVersion": "2026.1"
}
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The exact structure depends on the application.

The important part is that a report generated for 2026 should always be reproducible using the 2026 rule set.

If the rules change in 2027, the historical calculation should not silently change with them.

Why reproducibility matters

Imagine a user generates a report today.

Six months later, your application receives a tax-rule update.

If the user opens the old report again, should its numbers change?

Usually, no.

The report should preserve information such as:

  • tax year
  • rules version
  • calculation timestamp
  • source transactions
  • applied assumptions

That gives us something like:

Report
├── tax_year: 2026
├── rules_version: 2026.1
├── generated_at: ...
├── transactions: [...]
└── calculations: [...]
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Now the result can be reproduced later.

Rules and interpretation are not always the same thing

Another reason to avoid hardcoding everything into one calculation function is that some situations may require interpretation.

A system may have:

SUPPORTED
NEEDS_REVIEW
UNKNOWN
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instead of forcing every transaction into a definitive category.

For financial software, admitting that a case needs review can be safer than pretending every scenario has a perfectly deterministic answer.

Separate legislation from calculation code

Ideally, the calculation engine answers:

Given this rule set and these normalized transactions, what is the result?

It should not also be responsible for deciding which legislation is currently applicable.

That responsibility belongs to another layer.

A useful architecture might therefore look like:

Transactions
      ↓
Normalization
      ↓
Tax-year selection
      ↓
Rule-set resolver
      ↓
Calculation engine
      ↓
Report
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Each layer has one clear job.

Why this matters for Romania

Crypto transactions may look similar globally, but taxation is jurisdiction-specific and time-specific.

A transaction recorded by an exchange does not contain instructions saying:

"Apply Romanian rules for tax year 2026."

That context has to come from the application.

At The Crypto Support, separating transaction processing from versioned Romanian tax rules makes the system easier to update, test, and audit.

The goal is not only to calculate the current year correctly.

It is to still understand why an old report produced its result years later.

You can read the Romanian tax framework we use as context in our official guide:


Ghid Taxe Crypto România · The Crypto Support

How does your team handle frequent regulatory updates or changing compliance logic in your applications? Have you ever had to audit a historical calculation years down the road?

Let's discuss in the comments below! 👇

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