Calculation Methodology & Official Sources

Short answer: Every calculation runs locally in your browser using deterministic integer-cents arithmetic and official 2027 IRS and SSA figures.

1. Integer-Cents & Final-Paycheck Rounding

All dollar values are converted to integer cents before division. When dividing remaining annual room by remaining paychecks, the regular paycheck amount rounds down via Math.floor(remainingCents / remainingPaychecks), and the exact remainder is added to the final paycheck. This guarantees the annual total equals the limit to the cent without ever exceeding it (e.g., 25 × $980.76 + $981.00 = $25,500.00).

2. Pay-Date & 27-Paycheck Rules

Under 26 CFR 1.451-2 (constructive receipt), wages count in the calendar year they are actually paid. Because 2027 is not a leap year and January 1, 2027 is a Friday, biweekly schedules have 27 paydays (and weekly schedules have 53) only if the first 2027 payday falls on January 1, 2027.

3. Mandatory Roth Catch-Up Rule

Under SECURE 2.0 Section 603 (final regulations September 16, 2025, effective for taxable years beginning after December 31, 2026), if 2026 W-2 Box 3 FICA wages from the plan sponsor exceeded $155,000, any catch-up contributions above $25,500 are allocated as Roth.

4. Official Sources

• IRS Notice 2026-66 / IR-2026-136 (Nov 12, 2026): $25,500 elective deferral, $8,500 age 50+ catch-up, $11,750 ages 60–63 super catch-up, $75,000 Section 415(c) limit, $155,000 Roth catch-up wage threshold, $7,500 IRA limit.
• IRC Section 414(v)(2)(B)(i): Super catch-up replaces standard catch-up for ages 60–63; reverts at age 64.
• IRS Rev. Proc. 2026-35 (Nov 5, 2026): 2027 federal income tax brackets and standard deductions.
• SSA 2027 Wage Base (Oct 14, 2026): $192,300 OASDI wage base ($11,922.60 max employee tax).