Short answer
Enter the amount you actually paid under Gift Aid. The calculator multiplies it by 1.25: a £100 qualifying donation reduces estimated adjusted net income by £125. Do not enter the already grossed-up amount, and do not count a donation that was not made under Gift Aid.
Calculate the £100k effectUse the amount paid, not the grossed-up amount
HMRC’s adjusted-net-income method deducts the donation plus basic-rate tax. Enter £100 when that is the cash amount you paid under Gift Aid; the calculator divides by 0.8 and deducts £125. Entering £125 would gross up the same donation twice.
A £100,000 threshold example
If adjusted net income before Gift Aid is £100,125 and you paid a qualifying £100 donation, the £125 grossed-up deduction gives an estimate of exactly £100,000. That is at the childcare limit, not over it. The calculator still checks only the income condition, not full eligibility.
Check the donation and tax year first
Only include donations made under a valid Gift Aid declaration for the relevant tax year. You must have paid enough UK Income Tax or Capital Gains Tax to cover the amount charities reclaim. Timing elections, refunds, benefits linked to donations and joint payments can require separate checking; this calculator does not validate them.
Check the numbers with the full calculator
Compare both partners, pension methods, Gift Aid, Child Benefit, childcare income limits and the Personal Allowance taper in one place.
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