Estimate the sum calculator that shows work to find the approximate sum by rounding addends to the nearest 10, 100 or 1000. The step-by-step calculation help parents to assist their kids studying 3rd or 4th grade to verify the work and answers of estimate the sum by rounding addends to the nearest ten, hundred or thousand homework and assignment problems in pre-algebra or in number and operations in base ten (NBT) of common core state standards (CCSS) for mathematics.