Help with Calculation of TRS relief for 2009, husband moving off FTB status

I'm trying to calculate the TRS for next year ( approx given I don;t know the interest paid).

In 2009 I will be on Year 5 of a mortgage and husband on year 8.

Just wondering is the interest split in half or do I get the extra?

Say we pay €12,000 in interest for the year.

The cap is €3,000 for Non first time buyers and €10,000 for first time buyers.

Is our calculation 0.15 x €3,000 + 0.225 x €9,000

or 0.15 x €3,000 + 0.225 x €6,000?

Thanks