How to Calculate Years of Service from Hire Date

To calculate your years of service from your hire date, subtract the hire date from today (or from your last day of work if you’ve left), then adjust for any breaks in employment and for how your employer’s retirement plan defines a “year of service.” A rough answer is just the arithmetic. The number that actually controls your vesting, your FMLA eligibility, and your seniority depends on hours worked, protected absences, and which counting method the plan uses.

Pin Down Your Hire Date First

Your hire date is the first day you actually performed work for pay, not the day you signed an offer or accepted the job verbally. The federal Form I-9 uses this definition directly: employees complete Section 1 no later than their first day of employment, which the Department of Homeland Security defines as “the actual commencement of employment of an employee for wages or other remuneration.”¹ That makes the I-9 one of the most reliable records for the date your employment clock started.

If you can’t access your I-9, use your first pay stub or a signed employment contract showing your start date. When a digital HR portal shows a different date than paper records, go with whichever document ties directly to payroll enrollment or tax withholding.

For active employees, the end date of the calculation is today. For former employees, it’s the last day of work recorded in your personnel file. Your anniversary date is the month and day of your hire repeated each year, and it marks when another full year of service is complete.

Calculate It by Hand

Start with the simplest version: subtract the hire year from the current year. If you were hired in 2018 and it’s 2026, that gives you 8. That raw number assumes you’ve already passed your anniversary date this year. If you haven’t, subtract one.

For a more precise figure in years, months, and days, work through each unit separately. Subtract the hire day from today’s day. If today’s day is smaller, borrow 30 from the month column (treating each month as 30 days) and add it to the day. Then subtract the hire month from today’s month. If today’s month is now smaller because you borrowed, pull 12 from the year column. Finally subtract the years.

Suppose you were hired on September 15, 2019, and today is March 8, 2026. You can’t subtract 15 from 8, so borrow 30 days: 38 minus 15 gives 23 days. Your month column drops from 3 to 2, and you can’t subtract 9 from 2, so borrow 12 months: 14 minus 9 gives 5 months. Your year column drops from 2026 to 2025, so 2025 minus 2019 is 6 years. Result: 6 years, 5 months, 23 days.

One wrinkle catches people. If you were hired on February 29 during a leap year, your anniversary in non-leap years falls on either February 28 or March 1, depending on your employer’s policy or state law. Most HR systems default to March 1. Check your plan documents if a vesting or eligibility date hangs on the exact day.

Use a Spreadsheet for Multiple Employees or Fractional Years

Doing the arithmetic by hand across a department is a waste of time. Two functions in Excel and Google Sheets handle it automatically.

DATEDIF for Whole Years, Months, and Days

DATEDIF measures the gap between two dates in whatever unit you choose. The syntax is:

=DATEDIF(start_date, end_date, “unit”)

Replace “unit” with “Y” for completed years, “M” for completed months, or “D” for total days. To get a full year-month-day breakdown, combine three DATEDIF formulas: one with “Y,” one with “YM” (months remaining after full years), and one with “MD” (days remaining after full months).²

The most common error is a #NUM! result, which means the start date is later than the end date. Double-check that your hire date is in the first cell and today’s date is in the second, not the reverse. Use TODAY() as the end date if you want the calculation to refresh automatically.²

YEARFRAC for Decimal Years

YEARFRAC returns a decimal, which is useful when a benefit formula requires fractional years. The syntax is:

=YEARFRAC(start_date, end_date, [basis])

The optional “basis” argument controls day-counting. Leave it blank or set it to 0 for the default 30/360 convention, use 1 for actual days divided by actual days in the year, or use 3 for actual days divided by 365. For most HR purposes, basis 1 gives the most intuitive result. A value of 6.75 means about six years and nine months of service.

What Actually Counts as a Year of Service

Here’s where the raw calendar math stops being the whole answer. Under federal retirement plan rules, a “year of service” isn’t 12 months on the payroll. You need at least 1,000 hours of service during a 12-consecutive-month period for the year to count toward vesting.³ A part-time employee working 18 hours a week (about 936 hours a year) might never earn a year of service for vesting purposes, even after a decade on the payroll.

Plans can count in one of two ways, and which one your employer uses meaningfully changes where you stand.

Hours-of-Service Method

Under the default approach, the plan tracks actual hours worked plus hours for which you received pay (such as paid vacation or sick leave). You need 1,000 hours in a 12-month computation period to earn a year of service.⁴

When actual records aren’t maintained, federal regulations allow equivalency shortcuts. A plan can credit 10 hours for each day you’d be credited with at least one hour, or 45 hours for each such week.⁵ These equivalencies are generous. Someone working three days a week gets credited with 30 hours per week under the daily equivalency, which reaches 1,560 hours over a year, well above the threshold.

Elapsed-Time Method

The alternative skips hour-counting. Under the elapsed-time method, service runs continuously from your hire date (or rehire date) to your severance date, regardless of hours worked in between. A part-time employee gets the same credit as a full-timer. This is simpler to administer and more favorable for part-time workers, but employers aren’t required to use it.

Your plan’s summary plan description will say which method applies. If you’re part-time and trying to figure out whether you’ve hit a vesting milestone, this is the first thing to check.

Breaks in Service and Rehires

A gap in employment doesn’t automatically erase the years you’ve already banked. Federal law defines a “1-year break in service” as a 12-month period in which you complete no more than 500 hours of service.³ Working even a few weeks during a plan year can keep you above that line.

If you do hit a break, your pre-break years are frozen but not necessarily lost. Once you return and complete a new year of service, prior years generally get added back for vesting.⁶ The exception is severe: under a defined contribution plan, five consecutive one-year breaks in service let the employer permanently disregard your pre-break service. For nonvested participants, the threshold is the greater of five years or the years of service you had before the break.³ Someone who leaves after two years, stays away for six, and returns might find those first two years wiped from the vesting calculation.

When you’re rehired without a protected-leave exception, the gap generally needs to be subtracted from raw tenure. The standard approach: count the calendar days between the termination date and rehire date, then shift the original hire date forward by that many days. The result is an “adjusted service date” that reflects only active employment time. Payroll systems usually automate this.

Absences That Don’t Break Your Service

Certain absences get special treatment under federal law and don’t reduce your years of service.

Military service. The Uniformed Services Employment and Reemployment Rights Act treats time in the military as continuous employment. The period of absence is not a break in service, and on reemployment you step back onto the seniority ladder at the rung you would have reached had you stayed.⁷ This “escalator principle” extends to promotions, pay raises, and schedule improvements you would have received.⁸ Military time simply doesn’t get subtracted.

Federal workers’ compensation leave. Federal employees who miss time due to a compensable injury are generally entitled to full seniority credit for the entire absence upon returning to duty. The time counts toward within-grade increases, career tenure, leave accrual rates, and severance pay.⁹ Private-sector workers’ compensation rules vary by state and employer policy; no federal law requires private employers to credit that time.

FMLA Uses a Different Test

Years of service for the Family and Medical Leave Act don’t follow the retirement-plan definition. FMLA requires at least 12 months of employment with your current employer and at least 1,250 hours of service during the 12 months before leave begins.¹⁰ The 12 months don’t need to be consecutive, but the 1,250 hours must fall within the most recent year.

For employees returning from military service, USERRA protects this calculation. The months and hours you would have worked during deployment count toward FMLA eligibility as if you’d never left.⁷

Check the Employer’s Count Against Your Own

Federal law requires employers to maintain records sufficient for any employee to determine benefit rights under a retirement plan. Failing to keep those records or provide required information carries a civil penalty under ERISA Section 209.¹¹ More practically, incomplete employer records often push courts to resolve ambiguity in the employee’s favor.

If you suspect your years of service have been miscounted, request your plan’s individual benefit statement. You’re entitled to one annually for defined contribution plans. Compare it against your own records: hire date, rehire dates, leave periods, and hours worked. Discrepancies are far easier to fix while you’re still employed than after you’ve left and need the vesting credit.

1
U.S. Citizenship and Immigration Services. Completing Section 1, Employee Information and Attestation
2
Microsoft. DATEDIF Function
3
Office of the Law Revision Counsel. 26 USC 411 – Minimum Vesting Standards
4
Internal Revenue Service. Retirement Plans Definitions
5
eCFR. 29 CFR 2530.200b-3 – Determination of Service to Be Credited to Employees
6
eCFR. 29 CFR 2530.200b-4 – One-Year Break in Service
7
eCFR. 20 CFR 1002.210 – Seniority Rights Upon Reemployment Following Uniformed Service
8
eCFR. 20 CFR 1002.194 – Application of the Escalator Principle
9
eCFR. 5 CFR Part 353 – Restoration to Duty from Uniformed Service or Compensable Injury
10
U.S. Department of Labor. Fact Sheet #28 – The Family and Medical Leave Act
11
Office of the Law Revision Counsel. 29 U.S. Code 1059 – Recordkeeping and Reporting Requirements