The US tax system is pay-as-you-go. Employees pay through withholding; freelancers and investors usually pay quarterly estimates.
Why refunds are not a win
A large refund means you sent too much during the year. The money sat with the government instead of in a savings account.
Safe harbour
Penalties are generally avoided by paying either most of the current year tax or an amount based on last year's return. The exact thresholds change, so check the current year figures before relying on them.
Mixed income
If you have a job plus side income, raising withholding at the job is often simpler than filing quarterly estimates.
