401(k) Loan Payment Calculator and Repayment Estimate

This calculator estimates the level monthly payment and total interest for a fixed-rate 401(k) loan using the amount borrowed, annual percentage rate (APR), and repayment term. Enter the figures from your plan’s loan information to see the arithmetic; the estimate does not model plan-specific deductions or rules.

Formula

For a fixed rate and equal monthly payments, the payment is PMT = P × r ÷ [1 − (1 + r)⁻ⁿ]. Here, P is the amount borrowed in dollars, r is the monthly rate (APR ÷ 1,200), and n is the number of monthly payments (years × 12). The calculator rounds the payment to cents. Estimated total interest is rounded monthly payment × n − P, so it uses the rounded payment.

Worked Example

Using the defaults: P = $20,000, APR = 8%, and term = 5 years. The monthly rate is 8 ÷ 1,200 = 0.0066667, and n = 5 × 12 = 60.

Payment = 20,000 × 0.0066667 ÷ [1 − (1.0066667)⁻⁶⁰] = $405.53 per month, rounded to cents. Total interest = $405.53 × 60 − $20,000 = $4,331.80.

Assumptions

• The APR stays fixed for the full term.
• There are equal monthly payments, with the first payment one month after borrowing.
• Interest compounds monthly at APR ÷ 12.
• The estimate excludes plan fees, taxes, insurance, and other charges; none are inputs here.

Using a 401(k) Loan Payment Estimate

Use the borrowed amount, APR, and term shown in the plan’s loan documents or supplied by the plan administrator. A calculator cannot retrieve your plan’s terms. The default values are only a worked arithmetic example, not a rate or offer. Enter the APR as a percentage per year, such as 8 for 8%, and the repayment duration in years. The tool converts years to monthly payments.

The payment result is an estimated level monthly amount under the formula’s assumptions. Total interest is the difference between all rounded payments and the initial principal. A different payment schedule, a payment made on a different date, or plan-specific rounding can change the actual figures. If your plan quotes a payment per paycheck rather than monthly, compare the schedule with the administrator’s calculation instead of treating the monthly estimate as an exact payroll deduction.

What This Calculator Does Not Model

A 401(k) loan is tied to a particular workplace retirement plan, so this general calculator cannot represent every plan’s terms. It does not check whether a loan is permitted, calculate a maximum amount, show an account balance, or determine the effect on investments or retirement outcomes. It also does not account for payroll frequency, skipped or delayed payments, additional payments, fees, or changes to the repayment schedule.

Use plan documents or contact the plan administrator to confirm the amount, APR, payment frequency, due dates, and payoff figure that apply to your account. Any tax or legal consequences depend on individual circumstances and rules outside this calculator; this page does not assess them. Do not assume that the displayed monthly amount is the amount that will be withheld from each paycheck.

Common Input and Rounding Mistakes

Entering 0.08 instead of 8 means 0.08%, not 8%, because the APR field expects a percentage. Likewise, enter a five-year term as 5, not 60; the calculator converts it to 60 months. Use the amount actually borrowed rather than an account balance or a desired payment. Since displayed payments are rounded to cents, multiplying the rounded number can differ slightly from a calculation that keeps extra decimal places; this calculator deliberately uses the rounded payment for total interest.

How to Use This List

This page is one calculator, not a catalogue of plan options. Start with the loan amount and terms stated by your plan, then review both outputs: the monthly payment and estimated total interest. If you are comparing figures with a payroll schedule or official loan disclosure, match the same payment timing and rounding method. Ask the plan administrator about differences rather than changing inputs until the results appear to match.

Frequently Asked Questions

Does this calculate my exact 401(k) payroll deduction?
No. It estimates a monthly payment; payroll frequency, timing, and plan-specific calculations are not included.

Why does the result differ from my plan’s quote?
The plan may use different payment dates, rounding, fees, or a schedule other than equal monthly payments.

Should I enter my annual or monthly rate?
Enter the annual APR as a percentage; the formula divides it by 12 to obtain a monthly rate.

Does total interest include fees?
No. It is calculated from the rounded monthly payment and principal, with no fee input.

Can I use this to determine whether I qualify?
No. Eligibility and available loan terms are plan-specific and are not calculated here.

Final Thoughts

This calculator is for educational arithmetic, not financial advice. It cannot assess whether borrowing is appropriate for you. Its result is an estimate, and the lender’s disclosure gives the exact figures.

Related

• Budget Breakdown Sheet: Build and Use a Monthly Plan
• Budget Breakdown Slide: What to Include
• Budget Breakdown Planner: Plan Monthly Spending

in p | Loan amount | $ | 20000 | 1 | 100000000
in apr | Interest rate (APR) | % | 8 | 0.01 | 100
in yrs | Loan term | years | 5 | 0.0833 | 50
out pmt | Monthly payment | $ | p * (apr / 1200) / (1 - (1 + apr / 1200) ^ -(yrs * 12)) | 2
out int | Total interest | $ | pmt * yrs * 12 - p | 2