What is assumed, in words
Four assumptions are fixed for the whole projection, and they are assumptions rather than findings. First, the pay you type does not change. Second, the deferral percent and the match formula do not change. Third, the annual return you type is credited every year, compounded monthly, with no bad year and no good year. Fourth, the 2026 IRS dollar caps are used in year one and in every later year, even though the IRS adjusts those caps. If any of those is wrong for the question you are asking, the balance is the math of a different question. The page will not replace your return with a historical average. It does not have one it is willing to treat as yours.
Giuseppe Ilarda, the site owner, writes and checks the calculator. He does not hold out a credential or a professional finance background on the about page, and this projection does not create one. The disclaimer says the pages are educational estimates, not financial advice. Nothing here tells you to contribute a percent of pay, to take a match, or to expect a rate.
The 2026 limits the form actually uses
The IRS announced that the elective deferral limit for 2026 is $24,500.00 for 401(k), 403(b), governmental 457, and the Thrift Savings Plan. The same news release sets the general catch-up for people age 50 and over at $8,000.00, so the usual combined figure it states is$32,500.00. Notice 2025-67 states the section 402(g) limit as that $24,500.00 and the general catch-up as$8,000.00. The checkbox on this page adds only that general catch-up.
A higher catch-up applies for employees who are 60, 61, 62, or 63. For 2026 the IRS limits page puts that amount at $11,250.00 instead of $8,000.00. This calculator does not apply $11,250.00. Turning the box on is not a way to get it. If that higher cap is the one a plan allows, this page will understate the deferral a person in those ages could make. That omission is labeled so it is not mistaken for the limit itself.
The overall annual-additions limit on the same IRS page is $72,000.00 for 2026. The page says the limit covers elective deferrals other than catch-up, plus employer matching and nonelective contributions and forfeitures. It also describes $80,000.00including the general catch-up. This calculator uses that structure. Catch-up dollars sit outside the$72,000.00 room. Employer dollars are cut if they would push the non-catch-up deferral plus the employer amount over $72,000.00. Forfeitures and a nonelective contribution you did not type are not added.
A match, using the IRS example of 50 cents
The IRS contributions page says an employer can match elective deferrals if the plan allows it, and it gives the example of 50 cents for each dollar deferred. It does not say that plans match 50% or that they match up to a particular percent of pay. Those two numbers are inputs. On a typed pay of $100,000.00, a 6% deferral is $6,000.00. A match of 50% of deferrals up to 6% of pay is$3,000.00. Both are under the elective cap, so the cap does not move them. The form opens on a $10,000.00 balance, that pay, those percents, a 5% assumed return, and 10 years. Five percent is the same checkable assumption as the compound interest calculator, not a market view.
The growth step divides the annual employee plus employer amount by 12, rounds to the cent, and treats that as an end-of-month deposit. It then uses the monthly future-value formula from the compound page. Over many years the cent rounding of the monthly deposit can be a dollar or two away from twelve times the unrounded twelfth. The annual dollar labels on the result are the capped annual amounts, before that monthly rounding. The balance is the compounded series. Investor.gov's compound calculator is the public tool with the same kind of inputs for the growth piece. It does not apply IRS retirement limits. This page does.
What the caps do to a request that is too large
Ask for 20% of $500,000.00 with the age-50 box on, a match of 500% of deferrals up to 100% of pay, and a one-year projection at a zero return. The requested deferral is far above the elective cap. The employee amount stops at $32,500.00, which is $24,500.00 plus$8,000.00. The employer amount, before the annual-additions ceiling, would be several times that. The ceiling leaves $47,500.00 of employer money. Added together, employee and employer are $80,000.00, the figure the IRS limits page pairs with "including catch-up" next to the $72,000.00 overall limit. A 500% match is not a description of a normal plan. It is a test that the ceiling holds when the inputs ask for more than the published dollars.
The IRS also says the basic elective limit is the dollar amount or 100% of compensation, whichever is less. A deferral percent above 100 is rejected. Pay of zero produces a deferral of zero, and a balance you already have still compounds at the rate you type. The page does not add an IRA contribution. The 2026 IRA limit is in the IRS news release and is not modeled here, because an IRA is not a percent-of-pay match and this form would blur the two.
Taxes, and what the projection refuses to decide
A traditional deferral is generally excluded from income when it goes in, within the limit, and is taxed when it comes out. A designated Roth deferral is included in income now. The IRS contributions page draws that distinction. This projection never chooses. It also never withholds the deferral from a paycheck. Thepaycheck calculator is where a traditional 401(k) amount reduces wages for federal income tax and stays inside Social Security and Medicare wages, which is how Publication 15's wage table treats elective deferrals. Run the two pages separately. Do not add their results and call the sum a plan.
The balance is not reduced for income tax on withdrawals, for a penalty on an early distribution, or for investment fees. Social Security benefits are not estimated. A spouse's account is not included. Required minimum distributions are not computed. Those omissions are the point of an educational projection: the screen shows the compound path of the dollars and the caps, and it stops before it starts giving advice about a household. If the plan document defines the match on a different base, or vests the match over time, the employer line here is the formula you typed, not the document.