Step 1: Choose Your Calculation Mode

The calculator offers two modes depending on what information you have:

Annual Rent Mode

You know the Zone A rate (£ per square foot) and want to calculate the total annual rent. This mode also allows you to apply percentage-based adjustments for property characteristics.

Zone A Rate Mode

You know the total rent per annum and want to derive the implied Zone A rate. This is useful when analysing comparable evidence from known lettings.

Select your mode using the radio buttons at the top of the calculator. You can switch between modes at any time — the calculator will carry your values across where possible.

Step 2: Enter Your Primary Input

Depending on the mode selected:

• Annual Rent Mode — enter the Zone A rate in £ per square foot
• Zone A Rate Mode — enter the total rent per annum in £

Step 3: Enter Ground Floor Zone Areas

The calculator provides five standard zones with pre-set division factors following the halving-back convention:

Enter the area in square feet for each zone. You can adjust the division factors if your property uses non-standard zoning. The ITZA and rent for each zone are calculated automatically.

Leave a zone's area blank if it does not apply to your property.

Step 4: Add Adjustments (Annual Rent Mode Only)

Adjustments are percentage-based modifications that account for property characteristics affecting value. Click "+ Add Adjustment" to add one.

For each adjustment, specify:

• Reason — the factor being adjusted (Shape, Position in pitch, Frontage, Depth, Quantum, Lease terms, etc.)
• Applies to — which zone or the whole floor
• Percentage — positive values increase rent, negative values decrease it

Adjustments are not available in Zone A Rate mode, as that mode derives the rate from a known total rent.

Step 5: Add Ancillary Areas

Click "+ Add Area" to include additional space beyond the ground floor zones. Common ancillary areas include:

• First Floor, Second Floor, etc.
• Basement
• Mezzanine
• Gallery

For each ancillary area, enter the floor type, area in square feet, and an appropriate division factor. The division factor reflects the space's value relative to Zone A — higher factors mean lower relative value.

Step 6: Review the Summary

The summary section at the bottom displays three key figures:

Total NIA

The Net Internal Area — the sum of all physical floor areas entered

Total ITZA

The total "In Terms of Zone A" equivalent area across all zones and ancillary areas

Result

In Annual Rent mode: the calculated Rent per Annum. In Zone A Rate mode: the derived Zone A Rate.

Manual Override

If you need to enter a specific total rent or ITZA value (for example, to match a known transaction), tick the "Manually enter rent (ignore workings)" checkbox in the summary section. This lets you override the calculated values while keeping your zone data intact.

PDF Export

Click the "Download PDF" button to generate a professional report of your calculation. The PDF includes all zone details, adjustments, ancillary areas, and the summary — ready for client reports, rent review submissions, or file records.

Get Started

Ready to run a valuation? Open the ITZA Calculator and start entering your property details.

New to ITZA? Read our What is ITZA? guide for background on the method and the halving-back convention.