Some apps, such as Credit Karma and  Credit Sesame, suggest users open a new savings account that's affiliated with the app (but usually run by a bank) to help them put money toward savings. Simplifi doesn't offer any affiliated bank accounts, but it will do the bookkeeping for you if you want to set and contribute to savings goals. 

The best place to keep sinking funds is often a high-yield savings account.

If you’re saving for several different expenses, it’s worth checking with your financial institution to see if they offer savings accounts with customized buckets. This way, you only have one account to keep track of, but you’re still using the sinking fund strategy to save for specific future expenses.

Prepare for those inevitable expenses. When you see those tires are wearing thin, start saving for new ones. If you know the house you just bought has an old roof, start saving for a new one. These aren’t emergencies yet, and if you start saving up now, they never will be!

So with that in mind, the best option for sinking funds tends to be a high-yield savings account

You can create a sinking fund for any financial goal or expense you have. These can be ongoing expenses that occur irregularly, like car insurance that you pay every six months or once a year, or a big one-time expense, like a wedding.