How new phosphate targets may impact on your development

West Wales Calculator 

Our West Wales Calculator is now live.

Carmarthenshire’s original Nutrient Budget Calculator, the first in Wales, has been developed to form the West Wales Nutrient Budget Calculator. This calculator functions in the same way as the previous one but has additional features and has undergone refinement to cater to all three SAC catchments. This is an important first step in allowing nutrient neutral development to proceed in all catchments within West Wales.

This is a free resource, designed specifically for the Tywi, Teifi and Cleddau SAC catchments. It will support you to understand the impact of your development by confirming the proposed development’s total phosphorous budget, enabling you to consider the mitigation requirements. We have produced a Calculator Guidance document and a Calculator Technical Review as an instructional guide to help you use the calculator which also explains where data has been gathered from and how calculations have been deduced. Separate mitigation guidelines have been produced for each river catchment. These can be accessed here:

West Wales Mitigation Guidelines  

Although it is not required that you use this calculator, we strongly encourage you to do so.  Any applications submitted using alternative calculators will be subject to additional scrutiny to determine their relevance to conditions in the county.

If the answer is yes to either:

  • 1
  • 2 and 3
  • 2 and 4

Please use the West Wales nutrient budget calculator to assess whether development will increase nutrient loading to a European site/SAC and whether the development is within a catchment that drains to an affected European site.

  1. Whether the development is within a catchment that drains to an affected European site.
  2. Whether the receiving Wastewater Treatment Works discharges to an affected European site.
  3. Whether the development will lead to an increase in ‘overnight stays’.
  4. Whether the development will lead to an increase in the number of customers/users or employees coming into the catchment of the SAC river from outside of the catchment to work (in this context a user is defined as a person who may use a service or facilities provided by the development without being directly considered as a customer).


West Wales Calculator     Mitigation Guidelines

Calculator Guidance     Calculator Technical review


How it works

Simply input the information specific to your development, and site, into the calculator and work through the stages - instructions have been provided to help you. 

The calculator will produce a value of total phosphorus in kg per annum. This end value can be used to help you consider your phosphate mitigation options. However, the calculator will not estimate the amount of land required for any form of mitigation due to the numerous variables in nature-based solutions that may vary depending on proposed maintenance, maturity, and site-specific conditions.


The Local Authority does not accept liability for any direct or indirect damage, loss or inconvenience caused by the downloading and/or use of the Nutrient Budget Calculator.

The calculator will be subject to periodic reviews and updates to ensure it is based on the best available evidence and accurately reflects the local conditions. Please refer to the Calculator Guidance for an explanation of the data sets and methodology used in the calculator. If you have any comments, please let us know by emailing