SoloTaxKit.org Tax Planning & Estimation Tools

Smart U.S. Tax Calculators for Independent Earners

Free client-side tools built for U.S. freelancers, 1099 contractors, and solo pros. Compliant with IRS statutory guidelines. Runs entirely in your browser with zero logins and zero data tracking.

✓ U.S. Federal (IRS IRC)

✓ 100% Free & Private

✓ No Account or Sign-Up

✓ 2025 & 2026 IRS Tax Years

Tax Planning & Estimation Tools

Select a specialized tool below to model your specific situation.

IRS Form 8889 Rules

When do you need this? Switched Health Plans or Enrolled in an HDHP Mid-Year?

Prorated HSA Contribution Limit & Testing Period Calculator

Calculate your IRS Form 8889 Line 3 statutory contribution limit, evaluate the December 1st Last-Month Rule election, and model the 10% recapture penalty if HDHP coverage changes.

Target Audience: Employees changing jobs, newlyweds, parents, or anyone enrolling in a High Deductible Health Plan (HDHP) after January 1st.

Month-by-Month Coverage MatrixLast-Month Rule Dual Path10% Recapture Penalty SimulatorPaycheck Deduction Schedule

Launch HSA Calculator →

IRC § 6654 Safe Harbor

When do you need this? Freelancer or Side Hustler Planning Quarterly Estimated Taxes?

1099 Safe Harbor Quarterly Tax Estimator

Compare Prior-Year (100%/110%) and Current-Year (90%) statutory safe harbor targets, model year-end W-2 withholding cures, and estimate quarterly Form 1040-ES installments.

Target Audience: 1099 contractors, solopreneurs, side hustlers, and W-2 employees with variable secondary income.

Dual-Path 100%/110% vs 90%W-2 Late Withholding CureMissed-Quarter §6621 InterestPrintable 1040-ES Voucher Summary

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Why SoloTaxKit

Airtight Privacy Guarantee

Traditional tax calculators require email accounts, log personal tax data, or force bank connections via Plaid. SoloTaxKit runs entirely in browser memory. Disconnect your Wi-Fi—the calculation continues to work.

Statutory Accuracy

Calculations adhere strictly to current Internal Revenue Code sections, IRS Revenue Procedures (Rev. Proc. 2024-25 / 2025-XX), and Form 8889 / Form 1040-ES guidelines using decimal precision math.