Add tax support and partial split
There is a typical case I meet usually: I went to Walmart with my two roommates. X bought $10 things for himself, Y bought $12, Z bought $15. Meanwhile, we bought $30 things for sharing. And X paid the bill. Note that the money above didn't include the tax (I'm in US, one has to pay additional 8.75% tax of the original price). In this case we want to split the $30 and its tax equally, while each pay for his own thing including that tax. Since on the receipt the tax is only a sum, it's annoying for us to calculate the exact money (or the percentage) for each of us. I think it'll be great if we only need to input 1.the original money of each person, 2.the original money of the common part, 3.the taxincluded total money, 4.tax rate, and it'll automatically calculate how much one owes. This is also useful when we go to restaurant together and order separately. The key fact is that the tax makes calculation difficult..
Sorry for the trouble – I’ll pass on the feedback! For now, you could try adding your bill on our website and choosing “itemized bill” as the split method, which includes some handling for tax (and for splitting up a bill’s items between multiple people).

Poul Broechmann commented
When using CC in foreign currencies, you have to pay a small fee in local currency to the bank. In my case, I have to pay 0.13 DKK on top of the official exchange rate. I would like to propose that it will be possible to specify, per card, this small fee, when converting into local currency

Hildie commented
It would be nice to add tax percentage amount to an item before you split it.

ahchao commented
This features takes 3 months at most and it’s been more than 5 years. What gives?

Anirudh Ajith commented
Basically taxes of any kind are factored in. This way people will put in the amount of the item in the bill before tax, and the app can be used to calculate individual tax split based on the price.
Especially useful for restaurant bills where taxes are calculated on the total and the bill doesn’t reflect tax payment for individual items. 
Marli Olivier commented
There should be an option to add a % to each person’s individual spend for the service charge added to the bill.

Krishna Raj K commented
It'll be better if we can add a common expenditure(eg: delivery charge) in an unequally divided bill in which the common expenditure will be divided according to each person's percentage of share.
Also better if you add an option to input the tax percentage though each person's tax will be calculated automatically once saved.

Marc Leeb commented
when inputting restaurant bills and the like, it would be great if you could input the subtotal per person and the total tax and tip separately, and splitwise would divide the tax and tip by the percent of the subtotal.

Dominic Joseph commented
Would be better if there was a way to convert from specific unequal amounts to percentages. Like, my friends and I are at a restaurant, and we get the itemized receipt but we pay tax and tip in addition. We can add the itemized cost of each thing to Splitwise, but Splitwise doesn't have a way of changing those values to percentages of the whole. The reason we need percentages of the whole is to accurately calculate how much people owe for tax and tip.

Dina commented
Would love for the app to apply tax to my expense ie. I'm splitting my grocery bill and adding individual amounts and my settings would have my predefined "user" tax amount.
If you can get really fancy then you would have an option to somehow (smartly) have an override if you happen to be travelling and tax amounts change ... 
Dan Erez commented
many times we would like to split our bill before tax and only then add tax / tip per person ( buying at stores / eating at restaurants) . this could be implemented very simply by adding a pretax / post tax and tip button or adding tax by invited percent after the bill was split .

AdminSplitwise Support (, Splitwise) commented
From a UV ticket:
"It wil be best if you add tax benefits with tax as well as service tax and possible other tax" 
Qingquan Zhang (qqz) commented
this suggestion should be in another category..