How to handle travel expenses?

VAT deductibility: n/a (usually, there is no VAT on flights)

TAX deductibility: 100%

Flying to a conference, a client or another destination for professional purposes?
Your ticket is deductible for income tax (usually, there is no VAT on flights). Tickets for your partner, who travels with you to visit the country, are of course non-deductible.
Combining a business trip with a pleasure trip? You only deduct the airplane tickets that concern the professional part of your trip.

VAT deductibility: typically 100%

TAX deductibility: 100%

In terms of deductibility, public transport is an excellent option!
They are fully deductible (if the journey has a professional purpose, of course)
Note that the VAT on train tickets is 6%, but you will not necessarily see it indicated as such, the price of the SNCB ticket being inclusive of VAT.
In general, public transport companies are exempt from the obligation to issue users with an invoice for the delivery of tickets (tickets, cards, subscriptions). To recover VAT, your ticket will therefore be sufficient (this is an exception to the rule of proper invoices).

VAT deductibility: 0% (Reverse charge may apply)

TAX deductibility: 0% (Reverse charge may apply)

All tickets for train, subway, tram and bus trips outside Belgium.

VAT deductibility: typically 100%

TAX deductibility: 75%

You can deduct a taxi trip as long as, as always, you can prove the professional link: a taxi to the airport for a business trip is fine, a taxi back after dinner... does not work!
You get 75% back for income tax, 100% for VAT (if you have a valid invoice with your own VAT number).
Good news is that Uber is considered a taxi in terms of deductibility. The good thing? They can provide proper invoices.

VAT deductibility: 0%

TAX deductibility: 100%

Hotel fees must be: (i) necessary for business reasons, (ii) not to be unreasonable and (iii) If your other half travels with you, those costs are not deductible.
The daily allowances (for directors) that you grant yourself during your stay abroad for professional purposes are 100% deductible.
Any restaurant costs, if clearly stated on the hotel bill, are 69% deductible for income tax and are generally not deductible for VAT.

VAT deductibility: typically 100%

TAX deductibility: 100%

If you are travelling abroad for purely professional purposes, for example for training or prospecting, you deduct your transport and accommodation.
If you are self-employed in a company, you may be able to deduct per diems, a lump sum that covers e.g. your food and other expenses, under certain conditions.
If you are self-employed as a natural person, per diems do not apply. You can deduct professional expenses, with supporting documents as usual.