The amount you can claim back on travel expenses depends entirely on the purpose of the trip and the tax laws of your country. For business travel in the UK or the US, you can generally claim 100% of "reasonable and necessary" expenses, including flights, hotels, public transport, and business-related meals. If you use your own vehicle for work, you can claim a mileage allowance (as of 2026, the US IRS rate is roughly 67-70 cents per mile, while the UK HMRC rate is 45p per mile for the first 10,000 miles). If you are a traveler seeking a refund for a cancelled or delayed flight, you can claim back the full cost of your ticket or compensation ranging from $250 to $700 depending on the distance and length of delay under passenger rights like EU 261 or the US DOT rules. For your city and business data project, it is worth noting that most companies have their own internal "per diem" limits—for example, a $75 limit for daily meals. To maximize your claim, you must keep all physical or digital receipts, as tax authorities and corporate accounting departments will not reimburse "estimated" costs without proof of payment.