We applied based on my savings.
He needs to make a new application for tax credits because we're now married. This application form asks for details of income for partner, between April 2014 and April 2015. Given that I'm a US citizen and not a UK tax payer, we're not sure what to fill in. Do I have to put my income based on interest from savings too and then include some kind of note about my citizenship? Do I put anything being that I'm not a UK tax payer?
As you are now on a joint Tax Credits claim, I assume you must declare your savings especially as you used this for the financial requirements for your husband to show he could sponsor you. The £18,600 earnings to sponsor a partner is set at that amount to stop someone who sponsors from claiming Working Tax Credits: the WTC cut off is presently about 18k earnings for a couple, but that will reduce in April 2016 under the budget changes.
Savings reduce Tax Credit payments too. They don't calculate on the interest you actually earn from your savings but on a set formula they have to use, which is more than you will get in interest. I
think I read on a forum that it is a £1 reduction for each £250, but don't take my word for that. If it is, that will be a reduction in Working Tax Credit of £48 per week for savings of 62.5k in a full tax year.
You can't take the second adult element of WTC unless there is a child in the household, as you are subject to immigration control.
Although Tax Credits is an income based benefit, it has an anomaly that it is the only income based benefit that doesn't have a cut-off of 16k savings. When Tax Credits are replaced by Universal Credit, those with 16k in savings, capital, equity in land or a property they don't live in, will not be able to claim. Self empolyed claiming Universal Credit who declare they earn less than the hourly national minimum wage, will have their claim based on them earning the NMW, even if they don't earn that much.