Stimulus Check Plus-Up Payment Calculator: Compute How Much You'll Receive On top of tracking where and when your third stimulus check would be delivered, IRS gives you a new challenge of computing the right amount of payment you are entitled to receive. Luckily, we have a calculator that can do the math for you. Photo : Jeff Fusco/Getty Images On top of tracking where and when your third stimulus check would be delivered, IRS gives you a new challenge of computing the right amount of payment you are entitled to receive. You need to factor in the third stimulus check, plus your dependents and the newly approved "plus-up" payment factor.