Using the nutrient neutrality calculators
Source: gov.uk (2025-05-27)

How to use the calculators to work out a nutrient budget for residential developments in nutrient neutrality catchments.

Nutrient neutrality means that a new residential development will not cause increased nutrient pollution to specific protected sites.

Developers must use nutrient budget calculations to show that their proposals will not bring about a net increase in nutrient pollution to specific habitats sites. Some local planning authorities also have their own nutrient neutrality calculators which can be used.

The nutrient neutrality calculators are for:
- developers who need to complete a nutrient budget calculation to support a planning application
- local planning authorities who need to understand the mitigation requirements for future development or to assess planning applications
Summary of updates to the calculators

May 2025 updates

The calculators were updated in May 2025 to:
- reflect improvements that will be made to wastewater treatment works between 2025 and 2030 under the Water Industry National Environment Programme (WINEP)
- reflect earlier completion dates for select wastewater treatment work permit upgrades within the River Eden, River Mease and The Broads catchments
- remove the River Wensum calculator as it is included in The Broads calculator (this is now renamed The Broads and Wensum SACs calculator)
May 2024 updates

The calculators were updated in May 2024 to:
- reflect the list of wastewater treatment works under a duty to meet specified nutrient removal levels
- reflect updated advice for the Poole Harbour catchment
- correct a small number of minor data errors
27 nutrient neutrality catchments

The table shows the nutrient neutrality catchments (https://www.gov.uk/government/collections/tools-and-resources-for-calculating-nutrient-neutrality), the nutrients that apply and designated sensitive catchments.

A designated sensitive catchment area is one in which the water company must upgrade wastewater treatment works serving a population equivalent of over 2,000 to meet specified nutrient removal levels under the Water Industry Act 1991.

Find out more in the Notice of designation of sensitive catchment areas 2024 (https://www.gov.uk/government/publications/notice-of-designation-of-sensitive-catchment-areas-2024).

The calculators automatically take the upgrades into account.

About the calculator

Each calculator has a cover page of instructions and 5 worksheets to complete.

Worksheet 1: Nutrients from waste water

This worksheet calculates the increase in nutrient loading that comes from a development’s waste water.

Data inputs needed are:
- date of first occupancy
- occupancy rate
- daily water usage
- number of residential units
- wastewater treatment works name
Data outputs returned: nutrients from waste water.

Worksheet 2: Nutrients from current land use

This worksheet calculates the pre-existing nutrient load from current land use on the development site.

Data inputs needed are:
- catchment
- soil type
- rainfall
- NVZ (nitrate vulnerable zone)
- pre-development landcover type
- pre-development landcover area
Data outputs returned: nutrients from current land use.

Worksheet 3: Nutrients from future land use

This worksheet calculates the future nutrient load from land use on the development site after development.

Data inputs needed:
- after development land cover type
- after development land cover area
Data outputs returned: nutrients from future land use.

Worksheet 4: SuDS

This worksheet calculates the nutrient load removed from the implementation of sustainable urban drainage systems (SuDS).

Data inputs needed are:
- landcovers in SuDS catchment
- SuDS catchment area
- per cent of flow entering SuDS
- SuDS features
- removal rates
Data outputs returned: nutrients removed through SuDS.

Worksheet 5: Final nutrient budget

This worksheet calculates the net change in nutrient loading from the development to the habitats site with the addition of a buffer. The net change in nutrient loading plus the buffer is the nutrient budget.

Data outputs from worksheets 1 to 4 automatically calculate the final nutrient budget in worksheet 5.

Finding the data for your calculator

The sources for the data you need to fill in the calculator are listed in the cover sheet instructions.

It’s recommended that you collect all the data you need for each worksheet before you start filling it in.

Some of the data may be used in multiple worksheets. For example, the data you enter into worksheet 2 will be automatically used in worksheet 3 calculations as well.

Detailed steps for data in worksheet 2

Operational catchment:
- Go to the England Catchment Data Explorer (https://environment.data.gov.uk/catchment-planning/).
- Search the location by place name and postcode. This will give a high-level view of the area. Use the zoom feature to find the exact location of the development.
- Click on the light blue area on the map in which the development is located. This will bring the user to the operational catchment page.
- Make a note of the name of the operational catchment and select it from the dropdown list in the ‘Catchment’ cell when you get to this part of the calculator.
Soil drainage type associated with the predominant soil type within the development site:
- Go to the LandIS - Land Information System - Soilscapes soil types viewer (https://www.landis.org.uk/soilscapes/).
- Find your development site location on the map by using the search bar in the ‘Search’ tab. Searching a location should generate a pop-up window with the option to click ‘View soil information’. If this is not an option, click on the relevant soil type on the map and click on the ‘Soil information’ tab.
- In ‘Soil information’, go to the title ‘Drainage’ to find the ‘Soil drainage type’ value.
- Make a note of this soil type and select the relevant soil drainage type from the drop-down list in the ‘Soil drainage type’ cell when you get to this part of the calculator.
Annual average rainfall:
- Go to the National River Flow Archive. Select the relevant flow gauging station and find the ‘Catchment Info’. Each calculator has a link to the most downstream gauging station in the ‘About the calculator’ tab in the cover page. For example, Catchment Info for 42023 - Itchen at Riverside Park (ceh.ac.uk) (https://nrfa.ceh.ac.uk/data/station/spatial/42023).
- On the dropdown list in the ‘Catchment Info’ page, select ‘Rainfall’.
- Select the Legend tab.
- Zoom in on the map to find the location of the development and find the corresponding rainfall range from the Legend. Note that you cannot search the map using location information. You will need to move around the map to find your development site location.
- Make a note of the relevant rainfall band for your site and use it to select this rainfall band from the dropdown list.
Nitrate Vulnerable Zone (NVZ):
- Go to the UK Soil Observatory (bgs.ac.uk) (https://mapapps2.bgs.ac.uk/ukso/home.html?layers=NVZEng).
- Enter the location of the development site in the search bar.
- Once the area has been located, click on the map where the development is located to find out if it is within an NVZ.
- Make a note of this information. It will be needed to select ‘Yes’ or ‘No’ from the ‘Within Nitrate Vulnerable Zone (NVZ)’ cell when you get to this part of the calculator.
Filling in the worksheets

Read the instructions in the cover page and in each worksheet before you start.

Worksheet 1: Nutrients from waste water

Date of first occupancy

Some wastewater treatment works may be due an upgrade by 2025 or 2030 if they’re a designated sensitive catchment.

This means the amount of nutrient (and the amount of mitigation) may change over time, which will change the output from this stage of the calculations. The calculated values will change automatically and will show if there is an upgrade to a treatment works that affects the nutrient budget for your development.

Average occupancy rate

Enter the average occupancy rate of the development in:
- people per dwelling for residential dwellings
- units for other types of overnight accommodation, such as a hotel
The default setting for residential dwellings is 2.4 people per dwelling. Only change this value if there is good evidence that a different occupancy rate is appropriate.

For more information on selecting the right occupancy rates, visit Natural England’s Nutrient Neutrality Generic Methodology (https://publications.naturalengland.org.uk/publication/5143927928913920).

Number of dwellings or units

Enter the number of dwellings or units that will be in the development at the time of completion.

Wastewater treatment works connected to the development

You can find this information from the sewerage undertaker for the development site. If it is not feasible to connect to mains sewerage and you are using a septic tank (ST) or package treatment plant (PTP), select this option.

If the total nitrogen (TN) or total phosphorus (TP) final effluent concentrations (in mg/l) are specified by the manufacturer, select ‘Septic Tank user defined’ or ‘Package Treatment Plant user defined’ and enter the specified value in the cell where prompted.

If you do not have a TP or TN value provided by the manufacturer, select the ‘Septic Tank default’ or ‘Package Treatment Plant default’ option and a value will be provided automatically.

If an ST or PTP is being used, then a comprehensive maintenance regime is required as part of the application process. Consult your local planning authority for advice on how to specify this maintenance regime and demonstrate that it is appropriately secured. If the ST or PTP has phosphate-stripping capabilities, chemical dosing may be required. Chemical dosing requires a management plan to go with the planning application, outlining:
- how chemicals are stored
- dilution rates
- dosing frequencies
- how any chemicals used will not have an environmental impact
PTPs with chemical dosing may not be appropriate in all cases.

Worksheet 2: Nutrients from current land use

Calculate the annual nutrient load from existing (pre-development) land use on the development site.

Only enter data about the types and areas of land that are being altered by the development. For example, if 2 hectares of agricultural land within a 10-hectare development site are being kept in the same agricultural use, do not include this area in the calculations.

Existing land use types

In this column, each cell has a dropdown list of land use types. The list contains 7 agricultural land cover types to choose from and 8 different non-agricultural land cover types that may be present on a pre-development site.

Find out what land use types are within the development before you fill in the sheet. If there is a land use within the development area that is not in the list, select the most similar land use type. The table has a description of the different land use types you can choose from.

Worksheet 3: Nutrients from future land use

Calculate the annual nutrient load from new (post-development) land use on the development site.

You will need to select the type and area of the landcover present on the development site after the development has been completed.

In the ‘New land use types’ column, each cell has a dropdown list of 8 non-agricultural land use types that may be present on the post-development site. Find out what land use types are within the development before completing this column.

If there is a land use within the development area that is not in the list, select the most similar land use type.

Worksheet 4: SuDS

Calculate the nutrient load removed through sustainable urban drainage systems (SuDS). This sheet should only be used if SuDS are being implemented within the boundary of the development as part of the plan or project. The SuDS could be individual SuDS features, or multiple features combined in a management train. Larger developments may have several separate management trains serving different areas of the development site. The calculator allows data to be entered for each SuDS feature, or for the combined features in the management train.

The user must select which of the new land use types are within the SuDS train or feature catchment area. Each different land use type within a SuDS catchment should be entered on a new line.

Each landcover can be selected multiple times so that multiple SuDs trains or individual features within the development area can be included.

Enter in hectares the area of landcover within the SuDS catchment area.

Enter the percentage of the total surface flow within the SuDS catchment that will enter the SuDS train or feature. You will probably need a drainage assessment to determine the SuDS catchment area and the percentage of surface flows that will enter the SuDS.

You can include the name of the SuDS features or SuDS management train being used to treat the surface runoff. You can enter any text, allowing for entries of multiple SuDS within the development boundary.

Finally, enter the percentage removal rate of the SuDS features. Find out how to calculate the removal rates in the following guides published by the Construction Industry Research and Information Association (CIRIA) (https://www.ciria.org/CIRIA/Books/Bookshop.aspx?hkey=5d0b1bf4-bcee-4410-ade0-2dfb2a319cc2):
- using SuDS to reduce phosphorus in surface water runoff (C808)
- using SuDS to reduce nitrogen in surface water runoff (C815)
Present the design and SuDS removal rate calculations alongside the nutrient budget calculation.

The total nutrient load removed through all the SuDS will be automatically calculated.

Worksheet 5: Final nutrient budget

Worksheet 5 automatically uses the results from worksheets 1 to 4 to calculate the final nutrient budget for the site.

The output shows how much nutrient mitigation is required in kilograms per year to achieve nutrient neutrality.

If there are 2 values given because of an upgrade at the wastewater treatment works the development is connecting to, the calculator will show the nutrient mitigation needed both before and after the upgrade.

The output from worksheet 5 nutrient budget calculations is the balance of new sources of nitrogen and phosphorus from a development, minus the load removed through SuDS, and subtracting the existing sources of nitrogen and phosphorus from the pre-development site:

(Nutrients from waste water – Nutrients from current land use + (Nutrients from future land use – Nutrients removed through SuDS)) × 1.2 = Final nutrient budget.

To ensure the final figure is robust and precautionary, the balance is multiplied by 1.2 (to increase by a 20% buffer).

The 20% buffer accounts for uncertainties within the nutrient budget calculations and gives confidence that mitigation of the nutrient budget will remove the risk of adverse effects on site integrity in the habitats site.

Get help

If you still have questions about the nutrient neutrality calculators after reviewing this guidance, email xxx@xxx.xx (mailto:xxx@xxx.xx).