Can I raise tax on myself?

Question

I currently have a small realm in Ireland consisting of one duchy in which I have personal control over all the counties (i.e. my entire realm is my demesne). As such, I am the baron of every castle in my realm.

One of the laws I can pass is the option to collect tax from feudal lords (which gives some extra money, at the expense of a negative reputation effect from the lord holding the castle).

However, all of the castles are run by me - is it possible to tax myself in this way? Will the money come from the holding, or my treasury? Will there be any reputation effects? Or will nothing happen until I give up the barony to another lord?

If I pass this law, what will the effects be?

Answer 1

No, that law applies only to your vassals. Until you have castle vassals, the effect of that law will be nothing. You already receive the full income of your castle holdings anyway, so there's nothing to increase.

However, now is a good time to change your feudal tax laws to what you will want them to be once you start having feudal vassals, since you don't need anyone's approval to do so.

If you just need more income, set your steward to collecting taxes. You'll get a bump in revenues from that county, with a small chance of events that give you a lump sum or injure your steward. (If you don't like your steward, it's win-win!)

Answer 2

There will be no effect, as you already gain 100% of the feudal tax (see SevenSidedDie's answer). The tax revenue depends on the size of the holding, but is otherwise fixed. The taxation law only determines how much of that cake goes into your pockets rather than those of your vassal lord.

You can, however, raise the city tax or church tax if you are looking for more income. The latter is especially useful, if you have free investiture, as you can make all your mates bishops, so they will pay tax to you rather than the pope.

It's also worth noting, that raising the tax will lower the vassals opinion of you. This might mean that they will grant you a smaller levy, only pay their tax in part (!), or be more likely to rebel. Some times that doesn't matter (say, if you're really popular and/or possess a huge, bloodthirsty army), but if you're new on the throne and you're barely holding your realm together, perhaps it's better to keep your vassals happy ... for now.

The last point is that of ineffective taxation, since you mention that you have personal control over your entire realm. It might seem better to keep all (or most) the holdings for yourself, but when your realm grows over your demesne limit, it will lead to ineffective taxation. Basically, every holding above your limit leads to a penalty. Often, the gains from those extra counties are greater than the total penalty, but if you get too greedy, you will greatly suffer. It's possible to get a 100% tax penalty on yourself if you go 100% above your demesne limit.

Wikia has a good explanation on how tax is calculated.