Chumpynose

I keep going round in circles on this and am still confused. I've got a salary of £100k where I pay 10k into a workplace pension - deducted before tax. I have another income of around £16k with no pension deductions. So far net adjusted income of £106k If I pay 5k into a private pension with post tax income (multiplied by 1.25 - 6250) does my net adjusted income become £99,750 after self assessment and if so, is this taken into consideration when looking at tax free childcare/free childcare hours?