You can use the TurboTax TaxCaster estimated payments calculator to help determine how much your quarterly payments should be. Once you determine the annual total, simply divide the number by four to arrive at the amount to pay for each quarter.
Click this link to get started: https://turbotax.intuit.com/tax-tools/calculators/taxcaster/.
The maximum contribution limits to a SEP or SIMPLE IRA are as follows:
The contributions you make to each employee’s SEP-IRA each year cannot exceed the lesser of
You can put all your net earnings from self-employment in the plan: up to $12,500 (in 2015 - 2018), plus an additional $3,000 if you're 50 or older (in 2015 - 2018), plus either a 2% fixed contribution or a 3% matching contribution.
Additional note on Estimated Payments:
You may also calculate your estimated taxes from within the TurboTax software as well as prepare 1040-ES payment vouchers by following these TurboTax FAQ steps:
Rest assured that TurboTax 2017 uses the 2018 tax rates recently passed by Congress and signed into law when calculating your 2018 estimated taxes."