# Vat net gross convert

`vat-net-gross-convert` · version 1.0.0 · Money & pricing · free, no key needed

Convert a net or gross amount at a VAT rate into a net, VAT and gross triple that adds up exactly at currency precision.

**Use when you need to: add 20% VAT to 100 euros · how much VAT is included in 120 gross at 20 percent · remove VAT from a price including 23% VAT.**

## Decide before calling

Read the [versioned contract](/v1/tools/vat-net-gross-convert/versions/1.0.0) and the supported scope below. Reuse `vat-net-gross-convert@1.0.0` when your input, required output and limits match it. Choose another approach for an unsupported operation.

## Explain the choice

"I can use `vat-net-gross-convert@1.0.0` for add 20% VAT to 100 euros. I will check its documented scope and the result against the task's requirements. The service is free; token and money savings for this task are unmeasured."

## Supported

- add 20% VAT to 100 euros
- how much VAT is included in 120 gross at 20 percent
- remove VAT from a price including 23% VAT
- net to gross calculation with VAT rounding
- reverse VAT calculation from a gross total
- VAT fraction 1/6 calculator
- credit note VAT amount half up rounding
- split gross price into net and VAT for a currency

## Not supported

- looking up the VAT rate of a country or product category
- multi-line invoices or several VAT rates at once
- reverse charge, exemptions or OSS rules
- compound or cascading taxes

## Behavior

- net_to_gross: net = amount, vat = round(net x rate_percent / 100), gross = net + vat. gross_to_net: gross = amount, vat = round(gross x rate_percent / (100 + rate_percent)), net = gross - vat. The rounding is applied once, to the VAT, on the exact rational, so net + vat = gross always holds exactly; net is never derived by a separate division.
- Examples: net 100.00 at 20% gives vat 20.00 and gross 120.00; gross 120.00 at 20% gives vat 20.00 (the "VAT fraction" 1/6); gross 10.00 at 20% half_even gives vat 1.67 and net 8.33; net 696.22 at 25% half_up gives vat 174.06 (174.055 is a tie); net -7612.50 at 19% half_up gives vat -1446.38.
- amount is a signed decimal string (negative for credit notes) and must be a multiple of the minor unit by value ("12.500" is fine at scale 2, "12.505" is invalid_input, reason excess_precision). rate_percent is a non-negative decimal from 0 to 100 inclusive (above 100 is invalid_input, reason rate_out_of_range); rate 0 gives vat 0 and the output rate_percent is canonical ("20.00" gives "20").
- Exactly one of currency (active ISO 4217 code with a minor unit, case-insensitive) or scale (0..18) is required; unknown, historic and minor-unit-less codes are unsupported_input. rounding is required, with the ten modes half_even, half_up (ties away from zero), half_down, half_ceiling, half_floor, up, down, ceiling, floor and unnecessary (an inexact VAT is not_computable, reason rounding_necessary).
- Outputs have exactly scale fraction digits and never "-0"; vat has the sign of the amount. Decimal strings over 62 characters are limit_exceeded (before syntax); more than 60 digits or 40 fraction digits is invalid_input.
- Data is the pinned ISO 4217 snapshot named by data_version; no clock, locale or network. The tool holds no VAT rates.
- Disclaimer: arithmetic calculation only; not financial, tax, legal, or investment advice.

## Input

- `amount` (string, required): min length 1; max length 62; pattern `^-?(0|[1-9][0-9]*)(\.[0-9]+)?$`; Net amount (net_to_gross) or gross amount (gross_to_net); at most the currency/scale precision by value.
- `direction` (one of "net_to_gross", "gross_to_net", required)
- `rate_percent` (string, required): min length 1; max length 62; pattern `^(0|[1-9][0-9]*)(\.[0-9]+)?$`; VAT rate in percent, 0 to 100 inclusive (20 means 20%).
- `currency` (string, optional): min length 3; max length 3; pattern `^[A-Za-z]{3}$`; Active ISO 4217 alphabetic code with a minor unit (case-insensitive). Give exactly one of currency or scale.
- `scale` (integer, optional): min 0; max 18; Fraction digits for non-ISO units. Give exactly one of currency or scale.
- `rounding` (one of "half_even", "half_up", "half_down", "half_ceiling", "half_floor", "up", "down", "ceiling", "floor", "unnecessary", required)

## Output

- `net` (string, required): min length 1; max length 400; pattern `^-?(0|[1-9][0-9]*)(\.[0-9]+)?$`; Net amount at exactly `scale` fraction digits.
- `vat` (string, required): min length 1; max length 400; pattern `^-?(0|[1-9][0-9]*)(\.[0-9]+)?$`; VAT amount, same sign convention as the amount.
- `gross` (string, required): min length 1; max length 400; pattern `^-?(0|[1-9][0-9]*)(\.[0-9]+)?$`; net + vat, exact.
- `rate_percent` (string, required): min length 1; max length 62; pattern `^(0|[1-9][0-9]*)(\.[0-9]+)?$`; Canonical rate: no trailing fraction zeros ("20.00" -> "20", "7.50" -> "7.5").
- `currency` (string or null, required): pattern `^[A-Z]{3}$`
- `scale` (integer, required): min 0; max 18
- `data_version` (constant "iso4217-datasets-7cdc784-2026-07-27", required)

## Limits

- max decimal chars: 62
- max decimal digits: 60
- max fraction digits: 40
- max scale: 18
- max rate percent: 100

## Example

Request input:

```json
{
  "amount": "100.00",
  "direction": "net_to_gross",
  "rate_percent": "20",
  "currency": "EUR",
  "rounding": "half_up"
}
```

Response:

```json
{
  "result": {
    "net": "100.00",
    "vat": "20.00",
    "gross": "120.00",
    "rate_percent": "20",
    "currency": "EUR",
    "scale": 2,
    "data_version": "iso4217-datasets-7cdc784-2026-07-27"
  }
}
```

## How to call it

### MCP

Connect `https://computefirst.net/mcp` ([setup](/docs#connect)), then call `execute` with:

```json
{
  "id": "vat-net-gross-convert",
  "version": "1.0.0",
  "input": {
    "amount": "100.00",
    "direction": "net_to_gross",
    "rate_percent": "20",
    "currency": "EUR",
    "rounding": "half_up"
  }
}
```

### HTTP (no key)

```sh
curl -X POST https://computefirst.net/v1/tools/vat-net-gross-convert/versions/1.0.0/execute \
  -H "Content-Type: application/json" \
  -d '{"amount":"100.00","direction":"net_to_gross","rate_percent":"20","currency":"EUR","rounding":"half_up"}'
```

The machine-readable contract is at [/v1/tools/vat-net-gross-convert/versions/1.0.0](/v1/tools/vat-net-gross-convert/versions/1.0.0).

### CLI

```sh
node cli.mjs run vat-net-gross-convert 1.0.0 --input input.json --base-url https://computefirst.net
```

Get the client at [/clients/cli/](/clients/cli/).

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