Mental Rounding

Estimation relies on rounding strategically. Multiply 48 times 52? Think of it as roughly 50 times 50 which equals 2,500 (actual answer: 2,496). Need 15% of 80? Take 10% which is 8, then half of that for 5% which is 4, and add them: 12. Breaking complex numbers into friendly ones is the core estimation skill.

Strong estimators develop number sense — an intuition for magnitudes. They know that doubling a quantity ten times multiplies it by about a thousand, so small repeated growth piles up fast. They also keep a rough feel for how big a million, a billion, and a trillion really are. These instincts catch errors of ten or a hundred times that a spreadsheet might quietly hide.