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Income Taxes - Effective income tax rate (Details)

v3.21.2
Income Taxes - Effective income tax rate (Details) - Evolv Technologies Holdings Inc [Member]
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Reconciliation of the U.S. federal statutory income tax rate to the Company's effective income tax rate    
Federal statutory income tax rate 21.00% 21.00%
State income taxes, net of federal benefit 3.90% 1.90%
Federal and state research and development tax credits 7.30% 5.00%
Change in valuation allowance (33.70%) (23.20%)
Change in tax rate 1.30% (3.00%)
Permanent differences (0.30%) (1.40%)
Other 0.50% (0.30%)
Effective income tax rate 0.00% 0.00%