The basics are that the standard rate bands are €34k for single, €43k for married one income and €68k married 2 incomes.
So basically, out of your €34k, only €9k are transferrable.
Your personal credits are also transferrable, €1760. So your husband can avail of an extra €10760 credits from you not working. This is assuming you currently each use your own €34k at the moment, i.e. that you haven't already allocated the majority of the credits to him (or you).
Say you're both earning 40k. At the moment each pays 20% in tax on the first 34k and 41% on the rest, so each pays 6800 + 2460 = 9260. If you quit, he pays 20% of 40k = 8000. However if he currently earns 50k then he would have paid 6800 + 6560 = 13360 and now he pays 20% of 44760 (8952) + 41% of 5240 (2148) = 11100, i.e 2260 per annum less. So the exact figures depend on his current earnings. He'd also save on prsi and health levy.
What I don't know is what defines an income. I mean I assume that if you work one hour a week and earn €1000 per annum that that won't constitute married with 2 incomes thus giving you and extra €25k in credits. Perhaps someone else could explain this part?? And tell me if these figures are right??