Confused by Working Tax Credits

My partner and I have been receiving Working Tax Credits for the past 18 months as she worked full time (but on a low income) but I was unemployed.

However I have now found full time work myself (albeit on a low income too).

We've recently received our new tax credits assessment form through but it only lets you put what you earned the last tax year and not what your salary is this year.

So does that mean tax credits is based upon what you earned last year and not what you actually earn now?

Am a bit worried incase we keep getting them but then have to pay it all back next year or something!

Any help would be much appreciated!