How do I get formulas to calculate correctly?

I have used the following simple formula -

=T20*Z20

where t20 = =IF(N20100%,"0",K20-M20)
z20 = 917,000
n20 = 99.04%
k20=394
m20=390

When I do the math, it should total 3,668,000, yet my total in excel is
3,457,090. Why is excel calculating this incorrectly?