Using calculations in instructions

One of FilterWise's most powerful features is the ability to include mathematical calculations directly in your filter instructions. The AI can compute price per square meter, rental yield, monthly cash flow, and any other formula you describe.

How Calculations Work

When your instructions includes a formula, the AI:

Extracts the relevant values from the listing (price, surface area, rooms, etc.)
Applies the formula you described
Compares the result to your threshold
Reports the calculated value and whether it matches

You don't need to use any special syntax — just describe the calculation in plain language or with a simple formula.

Price Per Square Meter

The most common calculation. Instead of comparing total prices (which are meaningless without knowing the surface area), compare price per m².

Simple version:

Forward if price per square meter is below €7,000

The AI automatically divides the listing price by the surface area.

With context:

Forward if price per m² is at least 15% below the average for the neighborhood.
Use these averages:
- Paris 11th: €9,500/m²
- Paris 12th: €8,800/m²
- Paris 20th: €7,500/m²

Rental Yield

For investment properties, rental yield tells you the annual return relative to the purchase price.

Gross rental yield:

Forward if gross rental yield exceeds 5%.
Gross yield = (estimated annual rent / purchase price) × 100
Estimate monthly rent as: number of bedrooms × €550

Net rental yield (more accurate):

Forward if net rental yield exceeds 4%.
Net yield = ((annual rent - annual charges - property tax) / total acquisition cost) × 100
Estimate:
- Monthly rent = bedrooms × €600
- Annual charges = monthly charges × 12
- Property tax = 1 month of rent
- Total acquisition cost = price × 1.08 (including notary fees)

Monthly Cash Flow

Cash flow is the money left over after paying all expenses from rental income. Positive cash flow means the property pays for itself.

Forward if positive monthly cash flow exceeds €200.

Cash flow = Monthly rent - Loan payment - Monthly charges

Where:
- Monthly rent = (total rooms - 1) × €550
- Loan payment = monthly payment for a loan of (price × 1.08) over 25 years at 3.3%
- Monthly charges = as stated in listing, or estimate €150 if not mentioned

The PMT Formula

For loan calculations, you can reference the PMT formula (same as in Excel/Google Sheets):

Loan payment = PMT(rate/12, years×12, principal)

Example:

Forward if monthly cash flow > €300.

Revenue = (rooms - 1) × €500/month
Loan = PMT(3.3%/12, 25×12, price × 1.08)
Cash flow = Revenue - |Loan| - charges

Equivalent Excel: =PMT(3.3%/12, 300, price*1.08)

The AI understands the PMT function and computes it correctly, including converting annual rates to monthly.

Total Acquisition Cost

In many European countries, buying costs add 7-10% on top of the listed price:

Total cost = price × 1.08

This accounts for:

Notary fees (~3% for new builds, ~7-8% for older properties in France)
Agency fees (if not included in the listing price)

You can customize the multiplier based on your market.

Renovation Cost Estimates

Forward if price per m² AFTER renovation is still below €8,000.

Estimated price after renovation = (price + renovation cost) / surface
Renovation cost = surface × €1,200 (light renovation) or surface × €2,000 (full renovation)

Assume light renovation unless the listing mentions 'à rénover' or 'travaux importants'.

Combining Multiple Calculations

You can include multiple calculations in a single instructions:

Forward if the listing matches ANY of these:

1. Price per m² below €5,000 (bargain threshold)

2. Cash flow positive above €400/month:
   - Revenue = (rooms - 1) × €550
   - Loan = PMT(3.5%/12, 25×12, price × 1.08)
   - Cash flow = Revenue - |Loan|

3. After renovation value exceeds purchase cost by 20%:
   - Estimated value after reno = surface × €9,000 (area average)
   - Total cost = price × 1.08 + surface × €1,500
   - Margin = (Estimated value - Total cost) / Total cost × 100

Tips for Calculation Instructions

Define every variable: Don't assume the AI knows your local market conventions. Spell out every formula component.
Provide estimation rules: When a value isn't in the listing (e.g., rental income), tell the AI how to estimate it.
Use simple notation: rooms - 1, price × 1.08, rate/12 — the AI understands basic math notation.
Include the Excel equivalent: If you're describing a complex formula, adding the Excel equivalent helps the AI compute it correctly.
Test with known listings: Use the test panel to verify calculations against a listing where you've done the math manually.

Limitations

The AI performs calculations on values it can extract from the listing. If surface area isn't mentioned, it can't compute price per m².
Very complex multi-step formulas may occasionally produce rounding differences.
The AI doesn't have access to external data (market averages, tax rates) — you must provide these in your instructions.