CP2100 notice on your desk? Two dates and one number.

You type the date on your IRS CP2100 or CP2100A notice, how many payees it lists, and what you pay them. It returns the calendar date the B-notice must be mailed, the date backup withholding must begin, how many payees are still uncured, and the dollar liability you carry if you miss it.

US accounts-payable clerks, payroll administrators and information-reporting staff at companies that file Forms 1099. It is written for the person who just opened a CP2100 envelope, has a payee list in front of them, and needs to know which day the mailing is due and what the exposure is.

A free date calculator counts calendar days, not business days, and knows nothing about which day to count from. A chatbot will often quote 28 percent for backup withholding, the pre-sunset figure from older guidance. The IRS backup withholding C program page states 24 percent. Here the rate is a field you set, so the disagreement is visible instead of buried.

Every calculation is free and unlimited: both dates, the uncured payee count, the dollar liability, and the cure rule for first versus second notices. There is no watermark and no usage cap. The 60 dollar key adds two different things: exporting the per-payee register as a CSV file you keep, and setting browser alarms on both deadlines.

The comparison that matters is not a fee, it is the liability. Under IRC section 3406 the payer, not the payee, owes every dollar it failed to withhold. On the worked example shipped with this tool, twelve uncured payees at 12,500 dollars each at 24 percent is 36,000 dollars the payer pays from its own account, plus the interest that rides on it.