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Per diem definition

Per diem rates are a daily allowance determined by authorities at which companies can reimburse employees for business travel. By setting standardised rates and reducing the amount of documentation required, both governments and businesses enjoy a more efficient process.

The rules can seem complicated, with different rates for same-day and overnight stays, domestic and international travel, and with certain expenses excluded altogether. This brief guide explains how these rules work.

What does “per diem” mean?

“Per diem” is a Latin phrase meaning “by the day.” In today’s usage, it’s the daily allowance determined by governments and companies for business trips. When travelling for work, the employee is allowed to spend up to this amount without seeking specific approval for each purchase.

Why are per diem rates used?

Tracking and recording employee expenses is often tedious and time consuming — both for the company and the employees themselves. Both requesting permissions to spend and providing proofs of purchase create an administrative burden, and often lead to mistakes.

Per diem allowances let employees spend up to a fixed amount without approval, and often without providing receipts. (Whether proof is required may depend on your jurisdiction.) Because the amounts are small, it’s often not worth the time it takes to justify meal costs or incidental expenses.

Tax deductions

The financial reason companies use per diems is that they often offer tax deductions, therefore saving the company money. In most countries, legitimate business expenses are not taxed - including travel. But to streamline this process and provide guidelines, many governments determine and communicate the amount allowed.

In general, any travel expense which stays within the proscribed per diem rate will be free from tax. If companies choose to go over the allowed rate, the difference will be taxed.

How are per diem rates determined?

There are two basic ways in which a company will set per diem rates for employees:

  1. Following rates set by governments or authorities

  2. Setting its own rates if the official rates aren’t sufficient

Most companies will choose the rates set by official travel regulations. These ensure that you are eligible for tax deductions, and the rationale is clear for all employees. Some companies may choose to individual negotiate new rates with HMRC or the IRS, which naturally requires administrative and legal work.

Reimbursement rates in the UK

HMRC sets out what it calls “scale rate payments,” sometimes known as meal allowance rates. These include set rates for domestic travel during the day, overnight stays within the UK, and international travel. For the latter, each country (and sometimes city) has its own rate, reflecting the relative meal costs and lodging rates in those locations.

Here’s a full explanation of HMRC’s meal allowance rates.

Per diem rates in the US

The IRS sets out the federal per diem rates, broadly bucketed into either high cost or low cost localities. Each of these two buckets has a set daily rate which applies across all of the continental United States (CONUS). High cost localities are explicitly listed, meaning any location not on this list is considered low cost, and the lower rate applies.

There is also a separate rate for transportation professionals known as special M&IE (meal and incidental expenses), and a small rate of $5 per day for incidentals while traveling.

Read the US government guide to per diems

What can a per diem be used for?

Per diem rates only apply to business expenses, most often related to business travel. As such, employees should not use these pre-approved funds for entertainment outside of work, or to buy gifts or unnecessary personal items.

According to HMRC, business trips must fall into one of the following criteria:

  1. Journeys employees make in the performance of their duties (where travel is part of their duties)

  2. Journeys to or from a place they have to attend in the performance of their duties (travel to a place where attendance is in the performance of the duties).

So if travelling is your job, or if you have to visit a specific location in order to do your job, this is business travel.

In practice, this includes client visits, conferences, sales calls, and other legitimate meetings as part of your job. It specifically does not include travel to your “permanent workplace” (defined in the UK using the 24-month rule).

You should also exclude any expenses that aren’t explicitly related to performing your duties:


  • Travel excluding commute to and from permanent workplace.

  • Meals on work journeys outside normal commute.

  • Overnight accommodation on work journeys.


  • Normal commute to and from permanent workplace.

  • Parking fines, speeding tickets and other penalties.

  • Travel costs not exclusively for work e.g. top up of travel card also used for non-work.

What evidence is required?

Even though set rates help to reduce the administrative burden for both companies and governments, companies do still require some documentation to avoid tax on travel expenses.

In the US, per diem payments will be taxable if:

  • No expense report is filed with the employer,

  • The expense report filed does not include the date, time, place, amount and business purpose of the expense,

  • A flat amount is given to the employee and no expense report is required, or

If an adequate expense report isn’t provided and the company reimburses an employee, this is seen as extra wages. Therefore regular payroll taxes are applied, placing an extra burden on employees.

The rules are similar in the UK, although HMRC doesn’t routinely do “sampling exercises” with all companies to ensure compliance. Instead, “employers will still need to have a checking process in place, and be able to demonstrate that they satisfy the travel and subsistence rules.” Which likely amounts to the same requirements as for all business expenses: you should keep proofs of purchase and ideally file expense reports for every reimbursement.

How to manage per diems more effectively

Despite a streamlined system, employees still need to file some form of expense report to receive reimbursement. And companies need to process and pay these claims.

Most companies therefore still have an administrative hurdle to handle subsistence expenses. And the more manual the process - the more paperwork involved - the higher that hurdle.

Companies need a record of actual expenses to ensure that expenses are valid, but they also need to avoid a pile of receipts and manual data entry.

The best cure is smart expense report software. For travellers, the process is simple:

  • Incur an expense while travelling

  • Open the mobile app and take a photo of the receipt

  • The software reads the receipt and extracts all key details

  • The employee checks quickly and validates the expense claim

This is faster, easier, and far more accurate than waiting until the end of a month to submit dozens of claims at once.

And for finance teams, it’s even better:

  • You receive expense claims in real time, but can process them in bulk any time

  • Every receipt is safely stored from the moment the expense is incurred

  • There’s no data entry required

  • Reimburse employees directly from the platform, so no extra payroll run needed

The upshot is a far more efficient and robust expense claim process, with far less work required.

Per diems are meant to be simple and efficient. With a bit of automation and the right tools, they actually can be.

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Last update: 2 February 2022