Fostering and Your Benefits: What Changes and What Doesn’t

Fostering allowances are ignored when a means-tested benefit is worked out, so fostering rarely costs you your claim. The one thing that does need your attention is your State Pension, and this is why.
How Foster Carer Pay Works: The Fostering Allowance Explained

Greater London Fostering pays £479.50 a week for a child under 11 and £507.50 a week for a child aged 11 or over. Here is what that payment has to cover, why Qualifying Care Relief means most carers pay no tax on it, and what honestly happens to your income between placements.
Do Foster Carers Pay Tax? Qualifying Care Relief Explained

Tax is the part of fostering people worry about most, and it turns out to be simpler than they fear. A plain-English guide to Qualifying Care Relief, and why most carers pay little or nothing.